Mathematics Part Ii Chapter 10 Vector Algebra
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    NCERT Solution For Class 12 Mathematics Mathematics Part Ii

    Vector Algebra Here is the CBSE Mathematics Chapter 10 for Class 12 students. Summary and detailed explanation of the lesson, including the definitions of difficult words. All of the exercises and questions and answers from the lesson's back end have been completed. NCERT Solutions for Class 12 Mathematics Vector Algebra Chapter 10 NCERT Solutions for Class 12 Mathematics Vector Algebra Chapter 10 The following is a summary in Hindi and English for the academic year 2021-2022. You can save these solutions to your computer or use the Class 12 Mathematics.

    Question 1
    CBSEENMA12032684

    Find the area of the region bounded by the curve y= x and the lines x = 1, x = 4 and the x-axis in the first quadrant.

    Solution

    The equation of curve is y2 = x
    Required area = integral subscript 1 superscript 4 space straight y space dx space equals space integral subscript 1 superscript 4 square root of straight x space end root dx space equals integral subscript 1 superscript 4 straight x to the power of 1 half end exponent dx
                            equals space open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 1 superscript 4 space equals 2 over 3 open square brackets straight x to the power of 3 over 2 end exponent close square brackets subscript 1 superscript 4 space equals space 2 over 3 open square brackets open parentheses 4 close parentheses to the power of 3 over 2 end exponent minus 1 close square brackets
equals space 2 over 3 left parenthesis 8 minus 1 right parenthesis space equals space 2 over 3 cross times 7 space equals space 14 over 3 sq. space units.


     
    Question 2
    CBSEENMA12032685

    Find the area of the region bounded by y2 = 4 x, x = 1, x = 4 and the x-axis in the first quadrant.   

    Solution
    The equation of curve is y2 = 4 x
    Required area  = integral subscript 1 superscript 4 straight y space dx
                equals space integral subscript 1 superscript 4 2 square root of straight x space dx space equals space 2 integral subscript 1 superscript 4 straight x to the power of 1 half end exponent dx
equals space 2 open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 1 superscript 4 space equals space 4 over 3 open square brackets straight x to the power of 3 over 2 end exponent close square brackets subscript 1 superscript 4 space equals space 4 over 3 open square brackets open parentheses 4 close parentheses to the power of 3 over 2 end exponent minus 1 close square brackets
equals space 4 over 3 left parenthesis 8 minus 1 right parenthesis space equals space 4 over 3 cross times 7 space equals space 28 over 3 space sq. space units

    Question 3
    CBSEENMA12032686

    Find the area of the region bounded by y2 = 9x, x = 2, x = 4 and the x-axis in the first quadrant.

    Solution
    The equation of curve is y2 = 9x, which is right handed parabola.
    Two lines are x = 2,  x = 4.
        Required area = Area ABCD
                                equals space integral subscript 2 superscript 4 straight y space dx space equals space integral subscript 2 superscript 4 3 square root of straight x space dx space equals space 3 space integral subscript 2 superscript 4 straight x to the power of 1 half end exponent dx
space equals space 3 open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 2 superscript 4 space equals space 3 cross times 2 over 3 open square brackets straight x to the power of 3 over 2 end exponent close square brackets subscript 2 superscript 4
equals space 2. space open square brackets left parenthesis 4 right parenthesis to the power of 3 over 2 end exponent minus left parenthesis 2 right parenthesis to the power of 3 over 2 end exponent close square brackets space equals space 2 space left square bracket space 8 space minus square root of 8 right square bracket space equals space 2 left parenthesis 8 minus 2 square root of 2 right parenthesis
equals space left parenthesis 16 minus 4 square root of 2 right parenthesis space sq. space units.

    Question 4
    CBSEENMA12032687

    Find the area of the region bounded by y2 = x - 2, x = 4, x = 6 and the x-axis in the first quadrant.

    Solution

    The equation of curve is y2 = x - 2. which is right handed parabola with vertex at (2, 0).
    Two lines are x = 4 and x = 6
    Required area  = Area ABCD
                             equals space integral subscript 4 superscript 6 straight y space dx space equals space integral subscript 4 superscript 6 square root of straight x minus 2 end root dx
equals space integral subscript 4 superscript 6 left parenthesis straight x minus 2 right parenthesis to the power of 1 half end exponent dx
equals space open square brackets fraction numerator left parenthesis straight x minus 2 right parenthesis to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 4 superscript 6 space equals space 2 over 3 open square brackets left parenthesis straight x minus 2 right parenthesis to the power of 3 over 2 end exponent close square brackets subscript 4 superscript 6
equals space 2 over 3 open square brackets 4 to the power of 3 over 2 end exponent minus 2 to the power of 3 over 2 end exponent close square brackets space equals space space 2 over 3 left parenthesis 8 minus 2 square root of 2 right parenthesis space sq. space units


    Question 5
    CBSEENMA12032688

    Find the area under the given curves and given lines:
    (i) y = x2, x = 1, x = 2 and x-axis
    (ii) y - x4, x = 1, x = 5 and x -axis

    Solution

    (i) The given curve and lines are
    y = x2, x = 1, x = 2 and x-axis
    Required area = integral subscript 1 superscript 2 straight y space dx space equals space integral subscript 1 superscript 2 straight x squared dx space equals space open square brackets straight x cubed over 3 close square brackets subscript 1 superscript 2 space equals space 8 over 3 minus 1 third space equals space 7 over 3
    (ii) The given curve and lines are
     y = x4, x = 1, x = 5 and x-axis
    Required area  = integral subscript 1 superscript 5 straight y space dx space space equals space integral subscript 1 superscript 5 straight x to the power of 4 dx space space equals open square brackets straight x to the power of 5 over 5 close square brackets subscript 1 superscript 5 space equals space fraction numerator left parenthesis 5 right parenthesis to the power of 5 over denominator 5 end fraction minus fraction numerator left parenthesis 1 right parenthesis to the power of 5 over denominator 5 end fraction
space space space space space space space space space space space space space space space space space equals 3125 over 5 minus 1 fifth space equals space 3124 over 5 space sq. space units.

    Question 6
    CBSEENMA12032689

    Find the area of the region bounded by x2 = 4 y, y = 2, y = 4 and the y-axis in the first quadrant.

    Solution

    The equation of curve is x2 = 4y, which is an upward parabola.
    Lines are y = 2 and y  = 4
    Required area  = Area ABCD
                            equals space integral subscript 2 superscript 4 straight x space dy space equals space integral subscript 2 superscript 4 2 square root of straight y space dy
equals space 2 integral subscript 2 superscript 4 straight y to the power of 1 half end exponent dy space equals space 2 open square brackets fraction numerator straight y to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 2 superscript 4
equals space 4 over 3 open square brackets straight y to the power of 3 over 2 end exponent close square brackets subscript 2 superscript 4 space equals space 4 over 3 open square brackets left parenthesis 4 right parenthesis to the power of 3 over 2 end exponent minus left parenthesis 2 right parenthesis to the power of 3 over 2 end exponent close square brackets
equals space 4 over 3 left parenthesis 8 minus 2 square root of 2 right parenthesis space equals space fraction numerator 32 minus 8 square root of 2 over denominator 3 end fraction sq. space units


     

    Question 7
    CBSEENMA12032690

    Find the area of the region lying in the first quadrant and bounded by y = 4 x2, x = 0, y = 1 and y = 4.

    Solution
    The equation of parabola is straight y space equals space 4 space straight x squared space space space or space space straight x squared space equals space 1 fourth straight y comma space space which is upward parabola. The shape of straight x squared space equals space 1 fourth straight y comma space space straight x space greater or equal than 0 space is shown in the figure. 

    Required area ABCD = integral subscript 1 superscript 4 straight x space dy space equals space 1 half integral subscript 1 superscript 4 square root of straight y space dy
                                    equals space 1 half open square brackets fraction numerator straight y to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 1 superscript 4 space equals space 1 third open square brackets straight y to the power of 3 over 2 end exponent close square brackets subscript 1 superscript 4 space equals space 1 third open square brackets left parenthesis 4 right parenthesis to the power of 3 over 2 end exponent minus left parenthesis 1 right parenthesis to the power of 3 over 2 end exponent close square brackets
equals space 1 third left square bracket space 8 space minus space 1 right square bracket space equals space space 7 over 3 space sq. space units.
       
    Question 8
    CBSEENMA12032691

    Find the area of the region lying in the first quadrant and bounded by x2 = y - 3, y = 4, y = 6 and the y-axis in the first quadrant.

    Solution
    The equation of curve is x2 = y - 3. which is an upward parabola whose vertex is (0,3).
    Lines are y = 4,  y = 6
    Required area = Area ABCD
                             equals space integral subscript 4 superscript 6 straight x space dy space equals space integral subscript 4 superscript 6 square root of straight y minus 3 end root space dy
                                equals space integral subscript 4 superscript 6 left parenthesis straight y minus 3 right parenthesis to the power of 1 half end exponent dy space equals space open square brackets fraction numerator left parenthesis straight y minus 3 right parenthesis to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 4 superscript 6
equals space 2 over 3 open square brackets left parenthesis straight y minus 3 right parenthesis to the power of 3 over 2 end exponent close square brackets subscript 4 superscript 6 space equals space 2 over 3 open square brackets left parenthesis 3 right parenthesis to the power of 3 over 2 end exponent minus left parenthesis 1 right parenthesis to the power of 3 over 2 end exponent close square brackets
space equals 2 over 3 left parenthesis 3 square root of 3 space minus space 1 right parenthesis space sq. space units.

    Question 9
    CBSEENMA12032692

    Find the area of the region bounded by x2 = 16 y, y = 1, y = 4 and the y-axis in the first quadrant.

    Solution

    The equation of curve is
                      straight x squared space equals space 16 space straight y
    Required area = integral subscript 1 superscript 4 straight x space dy
                     equals space integral subscript 1 superscript 4 4 square root of straight y dy space equals space 4 integral subscript 1 superscript 4 straight y to the power of 1 half end exponent dy space equals space 4 open square brackets fraction numerator straight y to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 1 superscript 4
equals space 8 over 3 open square brackets straight y to the power of 3 over 2 end exponent close square brackets subscript 1 superscript 4 space equals space 8 over 3 open square brackets left parenthesis 4 right parenthesis to the power of 3 over 2 end exponent minus 1 close square brackets space equals space 8 over 3 left square bracket 8 minus 1 right square bracket space equals 8 over 3 cross times 7 space equals space 56 over 3 space sq. space units.

    Question 10
    CBSEENMA12032693

    Find the area bounded by the curve y2 = 4 a (x-1) and the lines x = 1 and y = 4 a.

    Solution
    The equation of parabola is y2 = 4 a (x-1)    ...(1)
    When y = 4 a , from (1) 16 a2 = 4 a (x-1)
    ⇒ x - 1 = 4 a ⇒ x = 4 a + 1
    therefore space space required space area space equals space integral subscript straight x space equals space 1 end subscript superscript straight x equals 4 straight a plus 1 end superscript straight y space dx space equals space integral subscript straight x equals 1 end subscript superscript straight x space equals space 4 straight a plus 1 end superscript 2 square root of straight a space square root of straight x minus 1 end root space dx open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
                           equals space 2 square root of straight a integral subscript 1 superscript 4 straight a plus 1 end superscript left parenthesis straight x minus 1 right parenthesis to the power of 1 half end exponent dx space equals space 2 square root of straight a open square brackets fraction numerator left parenthesis straight x minus 1 right parenthesis to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 1 superscript 4 straight a plus 1 end superscript
equals space fraction numerator 4 square root of straight a over denominator 3 end fraction open square brackets left parenthesis straight x minus 1 right parenthesis to the power of 3 over 2 end exponent close square brackets subscript 1 superscript 4 straight a plus 1 end superscript space equals space fraction numerator 4 square root of straight a over denominator 3 end fraction open square brackets left parenthesis 4 straight a right parenthesis to the power of 3 over 2 end exponent minus 0 close square brackets space equals space fraction numerator 4 square root of straight a over denominator 3 end fraction cross times 8 straight a to the power of 3 over 2 end exponent
equals space 32 over 3 space straight a squared space sq. space units
    Question 11
    CBSEENMA12032694

    Find the area of the region bounded by the curve straight y space equals space 2 square root of 1 minus straight x squared end root and x-axis. Draw a rough sketch..

    Solution
    The given equations are
    straight y space equals 2 square root of 1 minus straight x squared end root ...(1)
    (In the first quadrant)
    and y = 0    ...(2)
    [∴ x-axis has equation y = 0]
    From (1) and (2), we get,
                        0 space equals space 2 square root of 1 minus straight x squared end root space space space space space space space space rightwards double arrow space space space space space square root of 1 minus straight x squared end root space equals space 0
    rightwards double arrow space space space 1 minus straight x squared space equals space 0 space space space space space space space space space space space space rightwards double arrow space space straight x squared space equals space 1 space space space space space space space space rightwards double arrow space space space space straight x space equals space minus 1 comma space space 1
    Required area OAB = integral subscript 0 superscript 1 straight y space dx space equals space 2 integral subscript 0 superscript 1 square root of 1 minus straight x squared space end root space dx
                               equals space 2 space open square brackets fraction numerator straight x square root of 1 minus straight x squared end root over denominator 2 end fraction plus 1 half sin to the power of negative 1 end exponent straight x close square brackets subscript 0 superscript 1
equals space open square brackets straight x square root of 1 minus straight x squared end root plus sin to the power of negative 1 end exponent straight x close square brackets subscript 0 superscript 1
equals left parenthesis 0 plus sin to the power of negative 1 end exponent 1 right parenthesis space minus space left parenthesis 0 plus sin to the power of negative 1 end exponent 0 right parenthesis space equals space 0 plus straight pi over 2 minus left parenthesis 0 plus 0 right parenthesis space equals space straight pi over 2

    Question 12
    CBSEENMA12032695

    Calculate the area bounded by the parabola y2 = 4 a x and its latus rectum.

    Solution
    The equation of parabola is y2 = 4 a x.    ...(1)
    Let O be the vertex, S be the focus and LL' be the latus rectum of parabola.
    The equation of latus rectum is x = a.
    Also, we know that parabola is symmetric about x-axis.
    therefore space space space required space area space space equals space 2 space left parenthesis area space OSL right parenthesis
                                equals space 2 integral subscript 0 superscript straight a straight y space dx space equals space 2 space integral subscript 0 superscript straight a 2 square root of straight a space square root of straight x space dx
equals space 2 space.2 square root of straight a integral subscript 0 superscript straight a straight x to the power of 1 half end exponent dx space equals space 4 square root of straight a open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript straight a
equals space 4 square root of straight a.2 over 3 open square brackets straight x to the power of 3 over 2 end exponent close square brackets subscript 0 superscript straight a space equals space fraction numerator 8 square root of straight a over denominator 3 end fraction space open square brackets straight a to the power of 3 over 2 end exponent minus 0 close square brackets
equals space fraction numerator 8 square root of straight a over denominator 3 end fraction. straight a to the power of 3 over 2 end exponent space equals space 8 over 3 straight a squared space sq. space units.

    Question 13
    CBSEENMA12032696

    Give the rough sketch of the curve y2 = x and the line x = 4 and find the area between the curve and the line.    

    Solution
    The equation of parabola is
    y2 = x    ...(1)
    The equation of line is x = 4
    Also, we know that parabola is symmetric about x-axis
    therefore space space space required space area space equals space 2 space left parenthesis area space ORP right parenthesis
                       equals space 2 integral subscript 0 superscript 4 space straight y space dx space equals space 2 space integral subscript 0 superscript 4 square root of straight x space dx space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
                       equals space 2 space integral subscript 0 superscript 4 straight x to the power of 1 half end exponent dx space equals space 2 open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript 4 space equals space 4 over 3 open square brackets straight x to the power of 3 over 2 end exponent close square brackets subscript 0 superscript 4
space equals space 4 over 3 open square brackets 4 to the power of 3 over 2 end exponent minus 0 close square brackets space equals space 4 over 3 cross times square root of 64 space equals space 4 over 3 cross times 8 space equals space 32 over 3 space sq space. units.

    Question 14
    CBSEENMA12032697

    Find the area bounded between the curve y2 = x and the line x = 3. Draw the rough sketch also.    

    Solution

    The equation of parabola is
    y2 = x    ...(1)
    The equation of line is
    x = 3
    Also. we know that parabola is symmetric about x-axis.
    ∴ required area = 2 (area ORP)
    equals space 2 integral subscript 0 superscript 3 straight y space dx space equals space 2 space integral subscript 0 superscript 3 space square root of straight x space dx
equals space 2 space integral subscript 0 superscript 3 straight x to the power of 1 half end exponent dx space equals space 2 open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript 3 space equals space 4 over 3 open square brackets straight x to the power of 3 over 2 end exponent close square brackets subscript 0 superscript 3
equals space 4 over 3 open square brackets 3 to the power of 3 over 2 end exponent minus 0 close square brackets space equals space 4 over 3 cross times square root of 27 space equals space 4 over 3 cross times 3 square root of 3 space equals space 4 square root of 3 space sq. space units.

    Question 15
    CBSEENMA12032698

    The area between x = y2 and x = 4 is divided into two equal parts by the line x = a, find the value of a.

    Solution

    The equation of parabola is y2 = x
    From the given condition, area OAP under y2 = x between x = 0 and x = a = area ABQP under y2 = x between x = a and x = 4.
    therefore space space space integral subscript 0 superscript straight a straight y space dx space equals space integral subscript straight a superscript 4 space straight y space dx
rightwards double arrow space space integral subscript 0 superscript straight a square root of straight x space dx space equals space integral subscript straight a superscript 4 square root of straight x space dx
rightwards double arrow space space integral subscript 0 superscript straight a straight x to the power of 1 half end exponent dx space equals space integral subscript straight a superscript 4 straight x to the power of 1 half end exponent dx
rightwards double arrow space space open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript straight a space equals open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript straight a superscript 4 space space space space space space space space space space space space space space space space space space space space space space space space rightwards double arrow space space space space space space open square brackets straight x to the power of 3 over 2 end exponent close square brackets subscript 0 superscript straight a space equals space open square brackets straight x to the power of 3 over 2 end exponent close square brackets subscript straight a superscript 4
rightwards double arrow space space space space straight a to the power of 3 over 2 end exponent minus 0 space equals space 4 to the power of 3 over 2 end exponent minus straight a to the power of 3 over 2 end exponent space space space space space space space space space space space space space space space space space space space space space space space rightwards double arrow space space 2 space straight a to the power of 3 over 2 end exponent space equals space 8 space space space rightwards double arrow space space straight a to the power of 3 over 2 end exponent space equals space 4 space space space space rightwards double arrow space space straight a space space equals 4 to the power of 4 over 3 end exponent

    Question 16
    CBSEENMA12032699

    Find the area of the region bounded by the curve  y = x2 and the line y = 4.

    Solution

    The equation of parabola is
    y = x2    ...(1)
    The equation of line is
                    y = 4
    This parabola is symmetrical about y-axis
    therefore space space space requird space area space POQRP space equals space 2 space left parenthesis area space OQRO right parenthesis
                                               equals space 2 space integral subscript 0 superscript 4 straight x space dy space equals space 2 space integral subscript 0 superscript 4 square root of straight y space dy
equals space 2 integral subscript 0 superscript 4 straight y to the power of 1 half end exponent dy space equals space 2 open square brackets fraction numerator straight y to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript 4 space equals space 4 over 3 open square brackets straight y to the power of 3 over 2 end exponent close square brackets subscript 0 superscript 4 space equals space 4 over 3 open square brackets 4 to the power of 3 over 2 end exponent minus 0 close square brackets
space equals space 4 over 3 open square brackets left parenthesis 2 squared right parenthesis to the power of 3 over 2 end exponent minus 0 close square brackets space equals space 4 over 3 cross times 2 cubed space equals space 4 over 3 cross times 8 space equals space 32 over 3 space sq. space units

    Question 17
    CBSEENMA12032700

    Find the area of the region bounded by the curve y2 = 4x and the line x = 3.

    Solution

    The equation of parabola is
    y2 = 4 x
    The equation of line is
    x = 3
    Also, we know that parabola is symmetric about x-axis
    ∴ required area = 2 (area ORPO)

    equals space 2 integral subscript 0 superscript 3 2 square root of straight x space dx space equals space 4 space integral subscript 0 superscript 3 straight x to the power of 1 half end exponent dx
equals space 4 open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript 3 space equals space 8 over 3 open square brackets straight x to the power of 3 over 2 end exponent close square brackets subscript 0 superscript 3 space equals space 8 over 3 open parentheses 3 to the power of 3 over 2 end exponent minus 0 close parentheses space equals space 8 over 3 cross times square root of 27
equals space 8 over 3 cross times 3 square root of 3 space equals space 8 square root of 3 space sq. space units.

    Sponsor Area

    Question 18
    CBSEENMA12032701

    Using definite integrals, find the area of the circle x2 + y2 = a2.

    Solution

    The equation of circle is
    x2 + y2 = a2     ...(1)
    Its centre is a and radius a. We know that circle x2 + y2 = a2 is symmetrical about both axes.
    required area = 4 integral subscript 0 superscript straight a straight y space dx space equals space 4 space integral subscript 0 superscript straight a square root of straight a squared minus straight x squared end root dx
    space equals space 4 space open square brackets fraction numerator straight x square root of straight a squared minus straight x squared end root over denominator 2 end fraction plus straight a squared over 2 sin to the power of negative 1 end exponent straight x over straight a close square brackets subscript 0 superscript straight a
space equals space 4 open square brackets open parentheses 0 plus straight a squared over 2 sin to the power of negative 1 end exponent 1 close parentheses minus open parentheses 0 plus straight a squared over 2 sin to the power of negative 1 end exponent 0 close parentheses close square brackets space equals space 4 open square brackets straight a squared over 2 cross times straight pi over 2 close square brackets space space space left square bracket because space sin to the power of negative 1 end exponent 0 space equals space 0 right square bracket
equals space straight pi space straight a squared.

    Question 19
    CBSEENMA12032702

    Find the area of the region bounded by the ellipse straight x squared over 9 plus straight y squared over 4 space equals space 1.

    Solution

    The equation of ellipse is
                           straight x squared over 9 plus straight y squared over 4 space equals space 1
    or                   straight y squared over 4 space equals space 1 minus straight x squared over 9
    or              straight y squared space equals space 4 over 9 left parenthesis 9 minus straight x squared right parenthesis     
    therefore space space space space space straight y space equals space 2 over 3 square root of 9 minus straight x squared end root                                                       [In the first quadrant]
    The ellipse is symmetrical about both the axes
    ∴ required area = 4 (area AOB)
    equals space 4 integral subscript 0 superscript 3 space straight y space dx space equals space 4 cross times 2 over 3 integral subscript 0 superscript 3 square root of 9 minus straight x squared end root space dx space equals space 8 over 3 integral subscript 0 superscript 3 square root of left parenthesis 3 right parenthesis squared minus straight x squared end root dx
equals space 8 over 3 open square brackets fraction numerator straight x square root of left parenthesis 3 right parenthesis squared minus straight x squared end root over denominator 2 end fraction plus open parentheses 3 close parentheses squared over 2 sin to the power of negative 1 end exponent open parentheses straight x over 3 close parentheses close square brackets subscript 0 superscript 3
equals space 8 over 3 open square brackets open curly brackets fraction numerator 3 square root of 9 minus 9 end root over denominator 2 end fraction plus 9 over 2 sin to the power of negative 1 end exponent left parenthesis 1 right parenthesis close curly brackets space minus space open curly brackets 0 plus 9 over 2 sin to the power of negative 1 end exponent left parenthesis 0 right parenthesis close curly brackets close square brackets
equals space 8 over 3 open square brackets open curly brackets 0 plus 9 over 2 cross times straight pi over 2 close curly brackets minus open curly brackets 0 plus 9 over 2 cross times 0 close curly brackets close square brackets space equals space 8 over 3 cross times 9 over 2 cross times straight pi over 2 space equals space 6 space straight pi space sq. space units

    Question 20
    CBSEENMA12032703

    Find the area of the region bounded by the ellipse straight x squared over 16 plus straight y squared over 9 space equals 1.

    Solution
    The equation of ellipse is 
                  straight x squared over 16 plus straight y squared over 9 space equals 1
    or        straight y squared over 9 space equals space 1 minus straight x squared over 16
    or             straight y squared space equals 9 over 16 left parenthesis 16 minus straight x squared right parenthesis
    therefore space space space space space space straight y space equals space 3 over 4 square root of 16 minus straight x squared end root             ...(1)
    (in the first quadrant)
    The ellipse is symmetrical about both the axes.
    ∴    required area = 4 (area AOB)
    equals space 4 integral subscript 0 superscript 4 straight y space dx space equals space 4 integral subscript 0 superscript 4 3 over 4 square root of 16 minus straight x squared end root dx                       [because space of space left parenthesis 1 right parenthesis]
     equals 3 integral subscript 0 superscript 4 square root of left parenthesis 4 right parenthesis squared minus straight x squared end root dx space equals space 3 open square brackets fraction numerator straight x square root of 16 minus straight x squared end root over denominator 2 end fraction plus fraction numerator left parenthesis 4 right parenthesis squared over denominator 2 end fraction sin to the power of negative 1 end exponent open parentheses straight x over 4 close parentheses close square brackets subscript 0 superscript 4
equals space 3 open square brackets open curly brackets fraction numerator 4 square root of 16 minus 16 end root over denominator 2 end fraction plus 8 space sin to the power of negative 1 end exponent left parenthesis 1 right parenthesis close curly brackets minus open curly brackets 0 plus 8 space sin to the power of negative 1 end exponent 0 close curly brackets close square brackets
equals space 3 open square brackets open parentheses 0 plus 8 cross times straight pi over 2 close parentheses minus left parenthesis 0 plus 8 cross times 0 right parenthesis close square brackets space equals space 3 cross times 8 cross times straight pi over 2 space equals space 12 space straight pi space sq. space units. space

    Question 21
    CBSEENMA12032704

    Draw a graph of straight x squared over 9 plus straight y squared over 25 space equals space 1 and evaluate area bounded by it.

    Solution

    The equation of ellipse is
                     straight x squared over 9 plus straight y squared over 25 space equals space 1
    or                straight y squared over 25 space equals space 1 minus straight x squared over 9
    or                 straight y squared space equals space 25 over 9 left parenthesis 9 minus straight x squared right parenthesis
    therefore space space space space space straight y space equals space 5 over 3 square root of 9 minus straight x squared end root                     ...(1)
    (in the first quadrant)
    The ellipse is symmetrical about both the axes.
    ∴ required area = 4 (area AOB)
    equals space 4 integral subscript 0 superscript 3 straight y space dx space equals space 4 integral subscript 0 superscript 3 5 over 3 square root of 9 minus straight x squared end root space dx                                open square brackets because space of space left parenthesis 1 right parenthesis close square brackets space space
    equals space 20 over 3 integral square root of left parenthesis 3 right parenthesis squared minus straight x squared end root space dx space equals space 20 over 3 open square brackets fraction numerator straight x square root of 9 minus straight x squared end root over denominator 2 end fraction plus fraction numerator left parenthesis 3 right parenthesis squared over denominator 2 end fraction sin to the power of negative 1 end exponent open parentheses straight x over 3 close parentheses close square brackets subscript 0 superscript 3
equals space 20 over 3 open square brackets open parentheses fraction numerator 3 square root of 9 minus 9 end root over denominator 2 end fraction plus 9 over 2 sin to the power of negative 1 end exponent 1 close parentheses minus open parentheses 0 plus 9 over 2 sin to the power of negative 1 end exponent 0 close parentheses close square brackets
equals space 20 over 3 open square brackets open parentheses 0 plus 9 over 2 cross times straight pi over 2 close parentheses minus left parenthesis 0 plus 0 right parenthesis close square brackets space equals space 20 over 3 cross times fraction numerator 9 straight pi over denominator 4 end fraction space equals space 15 space straight pi space sq. space units.

    Question 22
    CBSEENMA12032705

    Using definite integrals, find the area of the ellipse straight x squared over 4 plus straight y squared over 9 space equals space 1

    Solution

    The equation of the ellipse is 
                              straight x squared over 4 plus straight y squared over 9 space equals space 1
    or                 straight y squared over 9 space equals space 1 minus straight x squared over 4
    or              straight y squared space equals space 9 over 4 left parenthesis 4 minus straight x squared right parenthesis
    therefore space space space space straight y space equals space 3 over 2 square root of 4 minus straight x squared end root                         ...(1)
    (in the first quadrant)
    The ellipse is symmetrical about both the axes,
    ∴ required area = 4 (area AOB)
    equals space 4 integral subscript 0 superscript 2 straight y space dx space equals space 4 space integral subscript 0 superscript 2 3 over 2 square root of 4 minus straight x squared end root dx                                       open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
    equals space 6 integral subscript 0 superscript 2 square root of left parenthesis 2 right parenthesis squared minus straight x squared end root space dx space equals space 6 open square brackets fraction numerator straight x square root of 4 minus straight x squared end root over denominator 2 end fraction plus fraction numerator left parenthesis 2 right parenthesis squared over denominator 2 end fraction sin to the power of negative 1 end exponent open parentheses straight x over 2 close parentheses close square brackets subscript 0 superscript 2
equals space 6 open square brackets open parentheses fraction numerator 2 square root of 4 minus 4 end root over denominator 2 end fraction plus 2 space sin to the power of negative 1 end exponent 1 close parentheses minus left parenthesis 0 plus 2 space sin to the power of negative 1 end exponent 0 right parenthesis close square brackets space equals space 6 open square brackets open parentheses 0 plus 2 cross times straight pi over 2 close parentheses minus left parenthesis 0 plus 0 right parenthesis close square brackets
equals space 6 straight pi space sq. space units.

    Question 23
    CBSEENMA12032706

    Draw a graph of straight x squared over 9 plus fraction numerator straight y squared over denominator 16 space end fraction space equals space 1 and evaluate area bounded by it.

    Solution
    The equation of ellipse is
                               straight x squared over 9 plus straight y squared over 16 space equals space 1
    or            straight y squared over 16 space equals space 1 minus straight x squared over 9
    or            straight y squared space equals space 16 over 9 left parenthesis 9 minus straight x squared right parenthesis
    therefore space space space space space space space straight y space equals space 4 over 3 square root of 9 minus straight x squared end root                        ...(1)
    (in the first quadrant)
    The ellipse is symmetrical about both the axes,
    ∴   required area = 4 (area AOB)
    equals space 4 integral subscript 0 superscript 3 space straight y space dx space equals space 4 integral subscript 0 superscript 3 4 over 3 square root of 9 minus straight x squared end root space dx                                [because space of space left parenthesis 1 right parenthesis right square bracket
    equals space 16 over 3 integral subscript 0 superscript 3 square root of left parenthesis 3 right parenthesis squared minus straight x squared end root space dx space equals space 16 over 3 open square brackets fraction numerator straight x square root of 9 minus straight x squared end root over denominator 2 end fraction plus fraction numerator left parenthesis 3 right parenthesis squared over denominator 2 end fraction sin to the power of negative 1 end exponent open parentheses straight x over 3 close parentheses close square brackets subscript 0 superscript 3
equals space 16 over 3 open square brackets open parentheses fraction numerator 3 square root of 9 minus 9 end root over denominator 2 end fraction plus 9 over 2 sin to the power of negative 1 end exponent 1 close parentheses minus space open parentheses 0 plus 9 over 2 sin to the power of negative 1 end exponent 0 close parentheses close square brackets
equals space 16 over 3 open square brackets open parentheses 0 plus 9 over 2 cross times straight pi over 2 close parentheses minus left parenthesis 0 plus 0 right parenthesis close square brackets space equals space 16 over 3 cross times fraction numerator 9 straight pi over denominator 4 end fraction equals space space 12 space straight pi space sq. space units.

    Question 24
    CBSEENMA12032707

    Using definite integrals, find the area of the ellipse straight x squared over straight a squared plus straight y squared over straight b squared equals 1.

    Solution

    The equation of the ellipse is
    straight x squared over straight a squared plus straight y squared over straight b squared space equals space 1           ...(1)
    The ellipse is symmetrical about the axes.
    ∴       required area = 4 (area OAB)
    equals space 4 integral subscript 0 superscript straight a straight y space dx space equals space 4 integral subscript 0 superscript straight a straight b over straight a square root of straight a squared minus straight x squared end root space dx                                   [because space of space left parenthesis 1 right parenthesis]
    equals space 4 straight b over straight a integral subscript 0 superscript straight a square root of straight a squared minus straight x squared end root dx
    equals 4 straight b over straight a open square brackets fraction numerator straight x square root of straight a squared minus straight x squared end root over denominator 2 end fraction plus straight a squared over 2 sin to the power of negative 1 end exponent straight x over straight a close square brackets subscript 0 superscript straight a
equals space fraction numerator 4 straight b over denominator straight a end fraction open square brackets open parentheses fraction numerator straight a square root of straight a squared minus straight a squared end root over denominator 2 end fraction plus straight a squared over 2 sin to the power of negative 1 end exponent straight a over straight a close parentheses minus open parentheses 0 plus straight a squared over 2 sin to the power of negative 1 end exponent 0 close parentheses close square brackets
equals space 4 straight b over straight a open square brackets open parentheses 0 plus straight a squared over 2. straight pi over 2 close parentheses minus left parenthesis 0 plus 0 right parenthesis close square brackets space equals space straight pi space straight a space straight b space sq. space units

    Question 25
    CBSEENMA12032708

    Sketch the region of the ellipse and find its area, using integration.
    straight x squared over straight b squared plus straight y squared over straight a squared equals 1.

    Solution

    The equation of ellipse is
                  straight x squared over straight b squared plus straight y squared over straight a squared space equals space 1 space space space or space space straight y squared over straight a squared space equals space 1 minus straight x squared over straight b squared space space or space straight y squared space equals space straight a squared over straight b squared left parenthesis straight b squared minus straight x squared right parenthesis
    therefore space space space space straight y space equals space straight a over straight b square root of straight b squared minus straight x squared end root space space space left parenthesis in space the space first space quadrant right parenthesis                          ...(1)
    The ellipse is symmetrical about both the axes.
    ∴ required area = 4 (area OAB)
    equals space 4 integral subscript straight a superscript straight b straight y space dx space equals space 4 space integral subscript straight a superscript straight b straight a over straight b square root of straight b squared minus straight x squared end root space dx
    equals space fraction numerator 4 straight a over denominator straight b end fraction integral subscript 0 superscript straight b square root of straight b squared minus straight x squared end root space dx                       open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
    equals space fraction numerator 4 straight a over denominator straight b end fraction open square brackets fraction numerator straight x square root of straight b squared minus straight x squared end root over denominator 2 end fraction plus straight b squared over 2 sin to the power of negative 1 end exponent open parentheses straight x over straight b close parentheses close square brackets subscript 0 superscript straight b
equals space fraction numerator 4 straight a over denominator straight b end fraction open square brackets open curly brackets fraction numerator straight b square root of straight b squared minus straight b squared end root over denominator 2 end fraction plus straight b squared over 2 sin to the power of negative 1 end exponent left parenthesis 1 right parenthesis close curly brackets minus open curly brackets 0 plus straight b squared over 2 sin to the power of negative 1 end exponent 0 close curly brackets close square brackets
equals space fraction numerator 4 straight a over denominator straight b end fraction open square brackets open curly brackets 0 plus straight b squared over 2. straight pi over 2 close curly brackets minus open curly brackets 0 plus 0 close curly brackets close square brackets space equals space fraction numerator 4 straight a over denominator straight b end fraction. fraction numerator straight pi space straight b squared over denominator 4 end fraction space equals space straight pi space straight a space straight b space sq. space units. space


    Question 26
    CBSEENMA12032709

    Find the area of the region in the first quadrant enclosed by the x-axis, the line straight x equals square root of 3 space straight y and the circle x2 + y2 = 4.

    Solution

    The equation of circle is
                       straight x squared plus straight y squared space equals space 4                      ...(1)
    The equation of line is
                          straight x space equals square root of 3 space straight y                       ...(2)
    From (1) and (2), we get,
                    3 straight y squared plus straight y squared space equals space 4 space space space space or space space space space 4 straight y squared space equals space 4
    therefore space space space space space space space space straight y squared space equals space 1
rightwards double arrow space space space space space space straight y space equals space 1 space space space space space space space space space rightwards double arrow space space space space space straight x space equals space square root of 3

    ∴     point of intersection of circle (1) and line (2) is P left parenthesis square root of 3 comma space 1 right parenthesis.
    From P, draw PM ⊥ x-axis.
    Also OA = radius of circle = 2
    ∴ A is (2, 0)
    Required area = Area OMAPO = Area of ∆OMP + area MAP
    = A1 + A2    ..(1 )
    where straight A subscript 1 space equals space area space of space increment OMP space equals space fraction numerator 1 over denominator square root of 3 end fraction integral subscript 0 superscript square root of 3 end superscript space straight x space dx

                    equals space fraction numerator 1 over denominator square root of 3 end fraction open square brackets straight x squared over 2 close square brackets subscript 0 superscript square root of 3 end superscript space equals space left parenthesis 1 right parenthesis space fraction numerator 1 over denominator 2 square root of 3 end fraction left parenthesis 3 minus 0 right parenthesis space equals space fraction numerator square root of 3 over denominator 2 end fraction
    and straight A subscript 2 space equals space integral subscript square root of 3 end subscript superscript 2 space straight y space dx space equals space integral subscript square root of 3 end subscript superscript 2 square root of 4 minus straight x squared end root space dx space equals space integral subscript square root of 3 end subscript superscript 2 square root of left parenthesis 2 right parenthesis squared minus straight x squared end root space dx
                 equals space open square brackets fraction numerator straight x square root of 4 minus straight x squared end root over denominator 2 end fraction plus fraction numerator left parenthesis 2 right parenthesis squared over denominator 2 end fraction sin to the power of negative 1 end exponent open parentheses straight x over 2 close parentheses close square brackets subscript square root of 3 end subscript superscript 2
equals space open parentheses fraction numerator 2 square root of 4 minus 4 end root over denominator 2 end fraction plus 2 sin to the power of negative 1 end exponent 1 close parentheses space minus space open parentheses fraction numerator square root of 3 space square root of 4 minus 3 end root over denominator 2 end fraction plus 2 space sin to the power of negative 1 end exponent fraction numerator square root of 3 over denominator 2 end fraction close parentheses
equals space open parentheses 0 plus 2 space cross times straight pi over 2 close parentheses space minus space open parentheses fraction numerator square root of 3 over denominator 2 end fraction plus 2 cross times straight pi over 3 close parentheses space equals space straight pi minus fraction numerator square root of 3 over denominator 2 end fraction minus fraction numerator 2 straight pi over denominator 3 end fraction space equals straight pi over 3 minus fraction numerator square root of 3 over denominator 2 end fraction
    therefore space space from space left parenthesis 1 right parenthesis comma space required space area space equals space fraction numerator square root of 3 over denominator 2 end fraction plus straight pi over 3 minus fraction numerator square root of 3 over denominator 2 end fraction equals space straight pi over 3 space sq. space units
                  
    Question 27
    CBSEENMA12032710

    Find the area of the region in the first quadrant enclosed by the x-axis, the line y = x, and the circle x2 + y2 = 32.  

    Solution

    The equation of circle is
                          straight x squared plus straight y squared space equals space 32                   ...(1)
    The equation of line is
                          y = x                                  ...(2)
    From (1) and (2), we get
                         straight x squared plus straight x squared space equals space 32 space space or space space 2 space straight x squared space equals space 16
    therefore space space space straight x squared space equals space 16 space space rightwards double arrow space space space space straight x space equals space 4 space space rightwards double arrow space space space straight y space equals space 4
    therefore     circle (1) and line (2) meet in P(4, 4)
    Radius OA of circle  = square root of 32 space equals space square root of 16 cross times 2 end root space equals space 4 square root of 2
    therefore space space space straight A space is space left parenthesis 4 square root of 2 comma space 0 right parenthesis
    Required area = Area OAP
                           = Area of increment OMP + area MAP
                           equals space straight A subscript 1 plus straight A subscript 2                                   ...(1)
    where straight A subscript 1 space equals space integral subscript 0 superscript 4 space straight y space dx space equals space integral subscript 0 superscript 4 straight x space dx space equals space open vertical bar straight x squared over 0 close vertical bar subscript 0 superscript 4 space equals space 1 half open square brackets 16 minus 0 close square brackets space equals space 8
          straight A subscript 2 space equals space integral subscript 0 superscript 4 square root of 2 end superscript straight y space dx space equals space integral subscript 0 superscript 4 square root of 2 end superscript square root of 32 minus straight x squared end root space dx space equals space integral subscript 4 superscript 4 square root of 2 end superscript square root of left parenthesis square root of 32 right parenthesis squared minus straight x squared end root space dx
                 equals space open square brackets fraction numerator straight x square root of 32 minus straight x squared end root over denominator 2 end fraction plus fraction numerator left parenthesis square root of 32 right parenthesis squared over denominator 2 end fraction sin to the power of negative 1 end exponent open parentheses fraction numerator straight x over denominator square root of 32 end fraction close parentheses close square brackets subscript 4 superscript 4 square root of 2 end superscript
equals space open square brackets fraction numerator 4 square root of 2 square root of 32 minus 32 end root over denominator 2 end fraction plus 32 over 2 sin to the power of negative 1 end exponent open parentheses fraction numerator 4 square root of 2 over denominator 4 square root of 2 end fraction close parentheses close square brackets minus open square brackets fraction numerator 4 square root of 32 minus 16 end root over denominator 2 end fraction plus 32 over 2 sin to the power of negative 2 end exponent open parentheses fraction numerator 4 over denominator 4 square root of 2 end fraction close parentheses close square brackets
space equals space left square bracket 0 plus 16 space sin to the power of negative 1 end exponent left parenthesis 1 right parenthesis right square bracket space minus space open parentheses fraction numerator 4 cross times 4 over denominator 2 end fraction plus 16 space sin to the power of negative 1 end exponent fraction numerator 1 over denominator square root of 2 end fraction close parentheses
equals space 16 space cross times space straight pi over 2 minus 8 minus 16 cross times straight pi over 4 space equals space 8 straight pi minus 8 minus 4 straight pi space equals 4 straight pi minus 8
    therefore space space from space left parenthesis 1 right parenthesis comma space we space get
space space space space space space required space area space equals space 8 space plus space 4 straight pi minus 8 space equals space 4 straight pi space sq. space units.

    Question 28
    CBSEENMA12032711

    Find the area bounded by the ellipse straight x squared over straight a squared plus straight y squared over straight b squared equals 1 space and space the spaceordinates x = a e and x = 0 where b2 = a2 (1 - e2) and e < 1.

    Solution

    The equation of ellipse
                       straight x squared over straight a squared plus straight y squared over straight b squared space equals space 1
    or      straight y squared over straight b squared space equals space 1 minus straight x squared over straight a squared
    or              straight y squared space equals space straight b squared over straight a squared left parenthesis straight a squared minus straight x squared right parenthesis
    or               straight y space equals space straight b over straight a square root of straight a squared minus straight x squared end root                             (in the first quadrant)
    Ordinates are x = 0,  x = a e.
    Required area = 2 space integral subscript 0 superscript straight a space straight e end superscript space straight y space dx            [because ellipse is symmetrical about x-axis]
                         equals space fraction numerator 2 straight b over denominator straight a end fraction integral subscript 0 superscript ae square root of straight a squared minus straight x squared end root dx space equals space fraction numerator 2 straight b over denominator straight a end fraction open square brackets fraction numerator straight x square root of straight a squared minus straight x squared end root over denominator 2 end fraction plus straight a squared over 2 sin to the power of negative 1 end exponent straight x over straight a close square brackets subscript 0 superscript straight a space straight e end superscript
equals space fraction numerator 2 straight b over denominator straight a end fraction open square brackets open curly brackets fraction numerator ae square root of straight a squared minus straight a squared straight e squared end root over denominator 2 end fraction plus straight a squared over 2 sin to the power of negative 1 end exponent open parentheses ae over straight a close parentheses close curly brackets minus open curly brackets 0 plus straight a squared over 2 sin to the power of negative 1 end exponent 0 close curly brackets close square brackets
equals space straight b over straight a open square brackets ae. straight a square root of 1 minus straight e squared end root plus straight a squared sin to the power of negative 1 end exponent left parenthesis straight e right parenthesis close square brackets space equals space ab space open parentheses straight e square root of 1 minus straight e squared end root plus sin to the power of negative 1 end exponent straight e close parentheses

    Question 29
    CBSEENMA12032712

    Find the area of the region bounded by the parabola y = x2 + 1 and the lines y = x, x = 0 and x = 2.

    Solution

    We are to find the area of the region bounded by the curves.
                                                straight y space equals space straight x squared plus 1 comma
straight y space equals space straight x comma
straight x space equals space 0
                                and          x = 2
                               Now   straight y space equals space straight x squared plus 1 is an upward parabola with vertex A (0, 1),  y  =x is straight line passing through the origin, B(2, 2) and lies below the parabola.
                     Now area bounded by the parabola, above the x-axis and ordinates x = 0, x = 2.
                          equals space integral subscript 0 superscript 2 left parenthesis straight x squared plus 1 right parenthesis space dx space equals space open square brackets straight x cubed over 3 plus straight x close square brackets subscript 0 superscript 2 space equals space open parentheses 8 over 3 plus 2 close parentheses space minus space left parenthesis 0 plus 0 right parenthesis space equals space 14 over 3
    Area bounded by the line y = x, above the x-axis and ordinates x = 0, x = 2.
                          equals space integral subscript 0 superscript 2 straight x space dx space equals space open square brackets straight x squared over 2 close square brackets subscript 0 superscript 2 space equals space 4 over 2 minus 0 space equals space 2
                    therefore space required space area space equals space 14 over 3 minus 2 space equals space 8 over 3 space sq. space units.

    Question 30
    CBSEENMA12032713

    Find the area of the region bounded by the curves y = x2 + 2, y = x, x = 0 and x = 3.

    Solution

    We are to find the area of the region bounded by the curves
    y = x2 + 2,
    y = x,
    x = 0
    and x = 3
    Now y = x2 + 2 is an upward parabola with vertex (0, 2).
    y = x is a straight line passing through the origin,
    (3, 3) and lies below the parabola.

    Now area bounded by the parabola, above the x-axis and ordinates x = 0, x = 3
    equals space integral subscript 0 superscript 3 left parenthesis straight x squared plus 2 right parenthesis space dx space equals space open square brackets straight x cubed over 3 plus 2 straight x close square brackets subscript 0 superscript 3 space equals space open parentheses 27 over 3 plus 6 close parentheses space minus space left parenthesis 0 plus 0 right parenthesis space equals space 15
    Area bounded by the line y = x, above the x-axis and ordinates x = 0, x = 3
                       equals space integral subscript 0 superscript 3 straight x space dx space equals space open square brackets straight x squared over 2 close square brackets subscript 0 superscript 3 space equals space 9 over 2 minus 0 space equals space 9 over 2
    therefore space space required space area space space equals space 15 space minus space 9 over 2 space equals space 21 over 2 space sq. space units. space

    Question 31
    CBSEENMA12032714

    Find the area of the region enclosed by the parabola y2 = 4 a x and the line y = mx.

    Solution
    The equation of parabola is y2 = 4 a x    ... (1)
    The line y = mx meets (1) where straight m squared straight x squared space equals space 4 space straight a space straight x
    or
       straight x space left parenthesis straight m squared straight x space minus space 4 straight a right parenthesis space equals space 0 space space or space straight x space equals space 0 comma space space fraction numerator 4 straight a over denominator straight m squared end fraction
    therefore space space straight y space equals space 0 comma space space fraction numerator 4 straight a over denominator straight m end fraction
    rightwards double arrow space space space straight O space is space left parenthesis 0 comma space 0 right parenthesis space space and space straight A comma space is space open parentheses fraction numerator 4 straight a over denominator straight m squared end fraction comma space fraction numerator 4 straight a over denominator straight m end fraction close parentheses
    Area bounded by curve (1) above the x - axis ordinates straight x space equals space 0 comma space space straight x space equals space fraction numerator 4 straight a over denominator straight m squared end fraction is
    equals space integral subscript 0 superscript 4 straight a divided by straight m squared end superscript straight y space dx space equals space integral subscript 0 superscript 4 straight a divided by straight m squared end superscript square root of straight x space dx space equals 2 square root of straight a open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript fraction numerator 4 straight a over denominator straight m squared end fraction end superscript
equals space fraction numerator 4 square root of straight a over denominator 3 end fraction open square brackets open parentheses fraction numerator 4 straight a over denominator straight m squared end fraction close parentheses to the power of 3 over 2 end exponent minus 0 close square brackets space space equals space fraction numerator 4 square root of straight a over denominator 3 end fraction cross times fraction numerator 8 straight a to the power of begin display style 3 over 2 end style end exponent over denominator straight m cubed end fraction space equals space 32 over 3 straight a squared over straight m cubed
    Area bounded by line y = m x, above the x-axis and ordinates x = 0,  straight x space equals space fraction numerator 4 straight a over denominator straight m squared end fraction space is
                         equals space integral subscript 0 superscript 4 straight a divided by straight m squared end superscript mx space dx space equals space straight m open square brackets straight x squared over 2 close square brackets subscript 0 superscript fraction numerator 4 straight a over denominator straight m squared end fraction end superscript space equals space straight m over 2 open square brackets straight x squared close square brackets subscript 0 superscript fraction numerator 4 straight a over denominator straight m squared end fraction end superscript
equals space straight m over 2 open square brackets fraction numerator 16 straight a squared over denominator straight m to the power of 4 end fraction minus 0 close square brackets space equals space straight m over 2 cross times fraction numerator 16 straight a squared over denominator straight m to the power of 4 end fraction space equals space fraction numerator 8 straight a squared over denominator straight m cubed end fraction space sq. space units
    therefore space space space required space area space equals space fraction numerator 32 space straight a squared over denominator 3 space straight m cubed end fraction minus fraction numerator 8 space straight a squared over denominator straight m cubed end fraction space equals space fraction numerator 32 straight a squared minus 24 straight a squared over denominator 3 straight m cubed end fraction space equals space fraction numerator 8 straight a squared over denominator 3 straight m cubed end fraction space sq. space units.

    Question 32
    CBSEENMA12032715

    Find the area bounded by the curve  y = x2 and the line y = x.
    OR
    Find the area of the region {(x. y): x2 ≤ y ≤ x}.

    Solution
    The given region is {(x, y): x2 ≤ y ≤ x}
    This region is the intersection of the following regions:
    straight R subscript 1 space equals space open curly brackets open parentheses straight x comma space straight y right parenthesis close parentheses space colon space straight x squared space less or equal than space straight y close curly brackets
straight R subscript 2 space equals space open curly brackets left parenthesis straight x comma space straight y right parenthesis space colon space straight y space less or equal than straight x close curly brackets
    Consider the equations
                       straight y space equals straight x squared                  ...(1)
      and            y = x                     ...(2)
    From (1) and (2), we get
                              straight x space equals space straight x squared space space or space space straight x squared minus straight x space equals space 0
    rightwards double arrow space space space space straight x left parenthesis straight x minus 1 right parenthesis space equals space 0 space space space space rightwards double arrow space space space space straight x space equals space 0 comma space space 1
    ∴    from (2), y = 0, 1
    ∴    curves (1) and (2) intersect in the points O (0, 0) and A (1, 1)
    Required area = area of the shaded region
    equals space integral subscript 0 superscript 1 straight x space dx space minus space integral subscript 0 superscript 1 straight x squared space dx space equals space open square brackets straight x squared over 2 close square brackets subscript 0 superscript 1 space minus space open square brackets straight x cubed over 3 close square brackets subscript 0 superscript 1
equals space open parentheses 1 half minus 0 close parentheses space minus space open parentheses 1 third minus 0 close parentheses space equals space 1 half minus 1 third space equals space fraction numerator 3 minus 2 over denominator 6 end fraction space equals space 1 over 6 space sq. space units.
    Question 33
    CBSEENMA12032716

    Using the method of integration find the area bounded by the curve |x| + |y| = 1.
    [Hint: The required region is bounded by lines x + y = 1, x– y = 1, – x + y = 1 and
    – x – y = 1].


    Solution

    The given curve is
    |x| + |y| = 1
    or ± x ± y = 1
    The given equation represents four lines
    x + y = 1, x - y = 1,
    - x + y = 1 and -x - y = 1
    which enclose a square of diagonal 2 units length.
     

    Required area is symmetrical in all the four quadrants.
    ∴     required area = 4 (area OAB)
    equals space 4 space integral subscript 0 superscript 1 left parenthesis 1 minus straight x right parenthesis space dx space equals space 4 space open square brackets straight x minus straight x squared over 2 close square brackets subscript 0 superscript 1 space equals space 4 open square brackets open parentheses 1 minus 1 half close parentheses minus left parenthesis 0 minus 0 right parenthesis close square brackets
equals space 4 space cross times space 1 half space equals space 2 space sq. space units. space

    Question 34
    CBSEENMA12032717

    Find the area of the region bounded by the line y = 3 x + 2, the x-axis and the ordinates x = - 1 and x = 1.

    Solution

    The equation of given line is
    y = 3 x + 2    ...(1)
    Consider the lines
    x = -1    ...(2)
    and    x = 1    ...(3)
    Line (1) meets x-axis where y = 0

    therefore  putting y = 0 in (1), we get,
           0 space equals space 3 straight x plus 2 space space space or space space straight x space space equals space minus 2 over 3
    therefore line (1) meets x-axis in straight A open parentheses negative 2 over 3 comma space 0 close parentheses
    Let line (1) meet lines (2) and (3) in B and D respectively. From B, draw BC ⊥ x-axis and from D, draw DE ⊥ x-axis.
    Required area = Area of region ACBA + area of region ADEA
    equals space open vertical bar integral subscript negative 1 end subscript superscript fraction numerator negative 2 over denominator 3 end fraction end superscript left parenthesis 3 straight x plus 2 right parenthesis space dx close vertical bar space plus space integral subscript negative 2 over 3 end subscript superscript 1 left parenthesis 3 straight x plus 2 right parenthesis space dx
equals space open vertical bar open square brackets fraction numerator 3 straight x squared over denominator 2 end fraction plus 2 straight x close square brackets subscript negative 1 end subscript superscript negative 2 over 3 end superscript close vertical bar space plus space open square brackets fraction numerator 3 straight x squared over denominator 2 end fraction plus 2 straight x close square brackets subscript negative 2 over 3 end subscript superscript 1
equals space open vertical bar open curly brackets 3 over 2 minus open parentheses negative 2 over 3 close parentheses squared plus 2 space open parentheses negative 2 over 3 close parentheses close curly brackets space minus space open curly brackets 3 over 2 left parenthesis negative 1 right parenthesis squared plus 2 left parenthesis negative 1 right parenthesis close curly brackets close vertical bar
space space space space space space space space space space space space space space space space space
                                                              plus open square brackets 3 over 2 left parenthesis 1 right parenthesis squared plus 2 left parenthesis 1 right parenthesis close square brackets space minus space open square brackets 3 over 2 open parentheses negative 2 over 3 close parentheses squared plus 2 open parentheses negative 2 over 3 close parentheses close square brackets
    equals space open vertical bar open parentheses 2 over 3 minus 4 over 3 close parentheses minus open parentheses 3 over 2 minus 2 close parentheses close vertical bar plus open parentheses 3 over 2 plus 2 close parentheses minus open parentheses 2 over 3 minus 4 over 3 close parentheses space equals space open vertical bar negative 2 over 3 plus 1 half close vertical bar plus open parentheses 7 over 2 plus 2 over 3 close parentheses
equals space open vertical bar negative 1 over 6 close vertical bar plus 25 over 6 space equals space 1 over 6 plus 25 over 6 equals space 26 over 6 equals space 13 over 3 space sq. space units.

    Question 35
    CBSEENMA12032718

    Find the area of the region included between the parabola straight y space equals 3 over 4 straight x squared space and space the space line space 3 straight x space minus space 2 straight y space plus space 12 space equals space 0

    Solution
    The equations of the given curves are
                     straight y equals space 3 over 4 straight x squared                          ...(1)
      and        3 straight x minus 2 straight y plus 12 space equals space 0             ...(2)
    From (2), 2 straight y space equals space 3 straight x plus 12
    therefore space space space straight y space equals space fraction numerator 3 straight x plus 12 over denominator 2 end fraction
    Putting this value of y in (1), we get,
                                      fraction numerator 3 straight x plus 12 over denominator 2 end fraction space equals 3 over 4 straight x squared
    therefore space space 6 straight x space plus 24 space equals space 3 straight x squared space space space space space rightwards double arrow space space straight x squared minus 2 straight x minus 8 space equals space 0 space space space space rightwards double arrow space space space space left parenthesis straight x plus 2 right parenthesis thin space left parenthesis straight x minus 4 right parenthesis space equals space 0
    rightwards double arrow space space space space straight x space equals space minus 2.4
therefore space space space space straight y space equals space 3 comma space 12
    therefore curves (1) and (2) intersect in points A (4, 12) and B(-2, 3).
    From A. draw AM ⊥ x -axis and from B, draw BN ⊥ x-axis.
    Required area = area of trapezium BNMA - (area BNO + area OMA)
    equals space 1 half left parenthesis 3 plus 12 right parenthesis space cross times 6 space minus space integral subscript negative 2 end subscript superscript 4 3 over 4 straight x squared dx                          open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
    equals space 45 space minus space 3 over 4 integral subscript negative 2 end subscript superscript 4 straight x squared dx space equals space 45 minus 3 over 4 open square brackets straight x cubed over 3 close square brackets subscript negative 2 end subscript superscript 4
equals space 45 minus 1 fourth open square brackets straight x cubed close square brackets subscript negative 2 end subscript superscript 4 space equals space 45 minus 1 fourth left square bracket 64 plus 8 right square bracket space equals space 27 space sq. space units. space

    Question 36
    CBSEENMA12032719

    Find the area bounded by the parabola x2 = 4 y and the straight line x = 4 y - 2.

    Solution

    The equation of curve is x2 = 4 y    ...(1)
    which is upward parabola with vertex O.
    The equation of line is
    x = 4 y - 2    ...(2)
    Let us solve (1) and (2)
    Putting x = 4y - 2 in (1), we get
                      left parenthesis 4 space straight y space minus 2 right parenthesis squared space equals space 4 space straight y
    therefore space space space 16 space straight y squared minus space 16 space straight y plus space 4 space equals space 4 straight y
therefore space space 16 space straight y squared minus 20 straight y space plus space 4 space equals space 0
or space 4 straight y squared minus 5 straight y plus 1 space equals space 0
therefore space space space space straight y space equals space fraction numerator 5 plus-or-minus square root of 25 minus 16 end root over denominator 8 end fraction space equals space fraction numerator 5 plus-or-minus 3 over denominator 8 end fraction space equals space 8 over 8 comma space 2 over 8
therefore space space space space straight y space equals space 1 comma space space 1 fourth
therefore space space from space left parenthesis 2 right parenthesis comma space space straight x space equals space 4 minus 2 comma space 1 minus 2 space equals space 2 comma space minus 1
therefore space space curve space left parenthesis 1 right parenthesis space and space line space left parenthesis 2 right parenthesis space intersect space in space two space points space straight A left parenthesis 2 comma space 1 right parenthesis space and space straight B space open parentheses negative 1 comma space 1 fourth close parentheses

    From A, draw AM ⊥ x-axis and from B. draw BN ⊥ x-axis.
    Required area = area AOB
    = Area of trapezium BNMA - (area BNO + area OMA)
    1 half open parentheses 1 plus 1 fourth close parentheses cross times 3 space minus space integral subscript negative 1 end subscript superscript 2 straight y space dx space equals space 1 half cross times 5 over 4 cross times 3 space minus space integral subscript negative 1 end subscript superscript 2 straight x squared over 4. dx              open square brackets because space space of space left parenthesis 1 right parenthesis close square brackets
    equals space 15 over 8 minus 1 fourth integral subscript negative 1 end subscript superscript 2 straight x squared space dx space equals space 15 over 8 minus 1 fourth open square brackets straight x cubed over 3 close square brackets subscript negative 1 end subscript superscript 2 space equals space 15 over 8 minus fraction numerator 1 over denominator 4 cross times 3 end fraction open square brackets straight x close square brackets subscript negative 1 end subscript superscript 2
equals space 15 over 8 minus 1 over 12 open square brackets left parenthesis 2 right parenthesis cubed minus left parenthesis negative 1 right parenthesis cubed close square brackets space equals space 15 over 8 minus 1 over 12 open square brackets 8 minus left parenthesis negative 1 right parenthesis close square brackets
equals space 15 over 8 minus 1 over 12 left parenthesis 8 plus 1 right parenthesis space equals space 15 over 8 minus 9 over 12 space equals space 9 over 8 space sq. space units. space

    Question 37
    CBSEENMA12032723

    Find the area of the region included between the parabola y2 = x and the line x + y = 2.

    Solution

    The equation of parabola is
    y2 = x    ...(1)
    The equation of line is
    x + y = 2    ...(2)
    From (2), y = 2 - x    ...(3)
    Putting this value of y in (1), we get,
    (2 - x)= x
    or x2 - 4 x + 4 = x or x2 - 5 x + 4 = 0


    ∴ (x - 1) (x - 4) = 0
    ∴ x = 1, 4
    ∴ from (3), y = 1, - 2
    ∴ parabola (1) and line (2) intersect in the points A (1, 1), B (4, - 1)
    Also line (2) meets x-axis in C (2,0)
    Required area is shaded.
    Area above x-axis = area AOL + area ALC
        equals space integral subscript 0 superscript 1 square root of straight x dx plus integral subscript 1 superscript 2 left parenthesis 2 minus straight x right parenthesis space dx space equals space 2 over 3 open square brackets straight x to the power of 3 over 2 end exponent close square brackets subscript 0 superscript 1 plus open square brackets 2 space straight x space minus space straight x squared over 2 close square brackets subscript 1 superscript 2
equals space 2 over 3 left parenthesis 1 minus 0 right parenthesis space plus space open square brackets left parenthesis 4 minus 2 right parenthesis space minus space left parenthesis 2 minus 1 half right parenthesis close square brackets space equals space 2 over 3 plus 2 minus 3 over 2 equals 2 over 3 plus 1 half equals 7 over 6 space sq. space units
    Area below x-axis = Area OBM - area CBM
                                 equals space integral subscript 0 superscript 4 square root of straight x minus integral subscript 2 superscript 4 left parenthesis 2 minus straight x right parenthesis space dx space equals space 2 over 3 open square brackets straight x to the power of 3 divided by 2 end exponent close square brackets subscript 0 superscript 4 space minus space open square brackets 2 straight x minus straight x squared over 2 close square brackets subscript 2 superscript 4
equals space 2 over 3 left square bracket 4 to the power of 3 divided by 2 end exponent minus 0 right square bracket space minus space open square brackets left parenthesis 8 minus 8 right parenthesis space minus space left parenthesis 4 minus 2 right parenthesis close square brackets
equals space 16 over 3 minus left parenthesis negative 2 right parenthesis space equals space 16 over 3 minus 2 space space space space space space space space space space space space space space left square bracket because space space area space is space always space positive right square bracket
equals space 10 over 3 space sq. space units
    therefore space space total space area space equals 7 over 6 plus 10 over 3 equals fraction numerator 7 plus 20 over denominator 6 end fraction equals 27 over 6 equals 9 over 2 space sq. space units. space

    Question 38
    CBSEENMA12032725

    Find the area of the region enclosed by the parabola x2 = y, the line y = x + 2 and the x-axis.
    OR
    Draw the rough sketch and find the area of the region:
    {(x, y): x2 < y < x + 2}

    Solution

    The equation of parabola is
    x2 = y    ...(1)
    The equation of line is
    y = x + 2    ...(2)
    From (1) and (2), we get,
    x2 = x + 2
    ∴ x2 - x - 2 = 0

    ⇒ (x - 2) (x + 1) = 0 ⇒    x = 2, -1
    ∴    from (2), y= 2 + 2, -1 +2 = 4, 1
    ∴  parabola (1) meets line (2) in two points A (2, 4) and B (-1. 1).
    From A. draw AM ⊥ x-axis and from B. draw BN ⊥ x-axis.
    Required area = Area AOB
    integral subscript negative 1 end subscript superscript 2 left parenthesis straight x plus 2 minus straight x squared right parenthesis space dx space equals space open square brackets straight x squared over 2 plus 2 straight x minus straight x cubed over 3 close square brackets subscript negative 1 end subscript superscript 2
    equals space open parentheses 4 over 2 plus 4 minus 8 over 3 close parentheses space minus space open parentheses 1 half minus 2 plus 1 third close parentheses space equals space 2 plus 4 minus 8 over 3 minus 1 half plus 2 minus 1 third equals 9 over 2 space sq. space units.

    Question 39
    CBSEENMA12032727

    Draw a rough sketch of the curves y = sin x and y = cos x as x varies from 0 to straight pi over 2 and find the area of the region enclosed by them and the x-axis.

    Solution

    Let OB and CA represent the curves y = sin x and y = cos x as x varies from 0 to straight pi over 2. The two curves intersect at D where
                                    sinx space equals space cosx space space space space space space space space space space rightwards double arrow space space space tanx space equals space 1 space space space space space space space space space space rightwards double arrow space space straight x space equals space straight pi over 4
    Required area = Area OAB + area OCA - area ODA
                             equals space integral subscript 0 superscript straight pi over 2 end superscript sinx space dx space plus space integral subscript 0 superscript straight pi over 2 end superscript cosx space dx minus integral subscript 0 superscript straight pi over 4 end superscript sinx space dx space minus integral subscript straight pi over 4 end subscript superscript straight pi over 2 end superscript cosx space dx
                              equals open square brackets negative cos space straight x space close square brackets subscript 0 superscript straight pi over 2 end superscript plus open square brackets sin space straight x close square brackets subscript 0 superscript straight pi over 2 end superscript minus open square brackets negative cos space straight x close square brackets subscript 0 superscript straight pi over 4 end superscript space minus space open square brackets sin space straight x close square brackets subscript straight pi over 4 end subscript superscript straight pi over 2 end superscript                          equals space open square brackets negative cos space straight pi over 2 plus cos space 0 close square brackets plus open square brackets sin space straight pi over 2 minus sin space 0 close square brackets space minus space open square brackets negative cos straight pi over 4 plus cos space 0 close square brackets minus open square brackets sin straight pi over 2 minus sin straight pi over 4 close square brackets
equals space left parenthesis negative 0 plus 1 right parenthesis plus left parenthesis 1 minus 0 right parenthesis minus open parentheses negative fraction numerator 1 over denominator square root of 2 end fraction plus 1 close parentheses space minus space open parentheses 1 minus fraction numerator 1 over denominator square root of 2 end fraction close parentheses
space equals square root of 2 space square space units.

                            
                               

    Sponsor Area

    Question 40
    CBSEENMA12032728

    Find the area bounded by the curve y = cos x between x = 0 and x = 2 straight pi.

    Solution

    The equation of curve is
    y = cos x
    Its rough sketch from x = 0 to x = 2 straight pi is shown in figure.

    Required area = area of the region OABO + area of the region BCDB + area of the region DEFD.
    equals space integral subscript 0 superscript straight pi over 2 end superscript cos space 2 straight x space dx space plus space open vertical bar integral subscript straight pi over 2 end subscript superscript fraction numerator 3 straight pi over denominator 2 end fraction end superscript cosx space dx close vertical bar space plus space integral subscript fraction numerator 3 straight pi over denominator 2 end fraction end subscript superscript 2 space straight pi end superscript space cos space straight x space dx
equals space open square brackets sin space straight x space close square brackets subscript 0 superscript straight pi over 2 end superscript space plus space open vertical bar open square brackets sin space straight x close square brackets subscript straight pi over 2 end subscript superscript fraction numerator 3 straight pi over denominator 2 end fraction end superscript close vertical bar space plus space open square brackets sin space straight x close square brackets subscript fraction numerator 3 straight pi over denominator 2 end fraction end subscript superscript 2 space straight pi end superscript
space equals space open parentheses sin space straight pi over 2 minus sin space 0 close parentheses space plus space open vertical bar open parentheses sin space fraction numerator 3 straight pi over denominator 2 end fraction minus sin space straight pi over 2 close parentheses close vertical bar space plus space open parentheses sin space 2 straight pi space minus space sin space fraction numerator 3 straight pi over denominator 2 end fraction close parentheses
equals space left parenthesis 1 minus 0 right parenthesis space plus space open vertical bar negative 1 minus 1 close vertical bar space plus space left parenthesis 0 plus 1 right parenthesis
equals space 1 plus open vertical bar negative 2 close vertical bar space plus space 1 space equals space 1 plus 2 plus 1 space equals space 4

    Question 41
    CBSEENMA12032730

    Find the area bounded by the curve y = sin x between x = 0 and x = 2 straight pi.

    Solution
    The equation of curve is y = sin x. Its rough sketch from x = 0 to x - 2 straight pi is shown is the figure.

    Required area = integral subscript 0 superscript straight pi space sinx space dx space plus space integral subscript straight pi superscript 2 straight pi end superscript left parenthesis negative sin space straight x right parenthesis space dx
                                          open curly brackets because space sin space straight x space greater or equal than 0 space for space straight x space element of space left square bracket 0 comma space straight pi right square bracket space and space sin space straight x space less or equal than space 0 space for space straight x space element of space left square bracket straight pi comma space 2 straight pi close curly brackets
                         equals space left square bracket negative cos space straight x right square bracket subscript 0 superscript straight pi plus open square brackets cos space straight x close square brackets subscript straight pi superscript 2 straight pi end superscript space equals space left parenthesis negative cos space straight pi space plus space cos space 0 right parenthesis space plus space left parenthesis cos space 2 straight pi space minus space cos space straight pi right parenthesis
equals space left parenthesis 1 plus 1 right parenthesis plus left parenthesis 1 plus 1 right parenthesis space equals space 4 space sq. space units.
    Question 42
    CBSEENMA12032732

    Using integration, find the area of the triangular region whose sides have the equations y = 2 x + 1, y = 3 x + 1 and x = 4.

    Solution

    The equations of the sides are
    y = 2 x + 1    ...(1)
    y = 3 x + 1    ...(2)
    and x = 4.    ...(3)
    Subtracting (1) from (2), we get,
                     0 space equals straight x space rightwards double arrow space space space straight x space equals space 0
    Putting x = 0  in (1), we get y = 0+1 = 1
    therefore   line (1) and (2) intersect in A(0, 1)
    From (1) and (3), we get,
                        straight x space equals space 4 comma space space straight y space equals space 8 space plus space 1 space equals space 9
    therefore space space line (1) and (3) intersect in B (4, 9)

    From (2) and (3), we get,
    x = 4, y = 12 + 1 = 13
    ∴  lines (2) and (3) intersect in C (4, 13)
    ∴ vertices of the triangle ABC are A(0, 1), B (4, 9), C (4, 13)
    Required area = Area of ∆ ABC = Area of region AOMC - area of region AOMB
    equals space integral subscript 0 superscript 4 left parenthesis 3 straight x plus 1 right parenthesis space dx space minus space integral subscript 0 superscript 4 left parenthesis 2 straight x plus 1 right parenthesis space dx space equals space open square brackets fraction numerator 3 straight x squared over denominator 2 end fraction plus straight x close square brackets subscript 0 superscript 4 space minus open square brackets fraction numerator 2 straight x squared over denominator 2 end fraction plus straight x close square brackets subscript 0 superscript 4
equals space open square brackets left parenthesis 24 plus 4 right parenthesis space minus space left parenthesis 0 plus 0 right parenthesis close square brackets space minus space open square brackets left parenthesis 16 plus 4 right parenthesis space minus space left parenthesis 0 plus 0 right parenthesis close square brackets
equals space 8 space sq. space units.

    Question 43
    CBSEENMA12032733

    Using the method of integration find the area of the region bounded by lines:
    2 x + y = 4, 3 x - 2 y = 6 and x - 3 y + 5 = 0.

    Solution

    The equations of the sides are
    2 x + y - 4 = 0    ...(1)
    3 x - 2 y - 6 = 0  ...(2)
    x - 3 y + 5 = 0    ...(3)
    Solving (1) and (2), we get
                fraction numerator straight x over denominator negative 6 minus 8 end fraction equals fraction numerator straight y over denominator negative 12 plus 12 end fraction equals fraction numerator 1 over denominator negative 4 minus 3 end fraction space space space space or space space fraction numerator straight x over denominator negative 14 end fraction equals straight y over 0 equals fraction numerator 1 over denominator negative 7 end fraction
    therefore space space space space space space space straight x space equals space fraction numerator negative 14 over denominator negative 7 end fraction space equals space 2 comma space space space space straight y space equals space fraction numerator 0 over denominator negative 7 end fraction space equals space 0
    therefore space space space space lines space left parenthesis 1 right parenthesis space and space left parenthesis 2 right parenthesis space intersect space in space straight C left parenthesis 2 comma space 0 right parenthesis
    Solving (2) and (3), we get,
                                      fraction numerator straight x over denominator negative 10 minus 18 end fraction equals fraction numerator straight y over denominator negative 6 minus 15 end fraction equals fraction numerator 1 over denominator negative 9 plus 2 end fraction space space space or space space fraction numerator straight x over denominator negative 28 end fraction equals fraction numerator straight y over denominator negative 21 end fraction equals fraction numerator 1 over denominator negative 7 end fraction
    therefore space space space space space space space space space straight x equals fraction numerator negative 28 over denominator negative 7 end fraction space equals 4 comma space space space space straight y space equals space fraction numerator negative 21 over denominator negative 7 end fraction space equals space 3
    therefore space space space space lines space left parenthesis 2 right parenthesis space and space left parenthesis 3 right parenthesis space intersect space in space straight A left parenthesis 4 comma space 3 right parenthesis
    Solving (1) and (3), we get,
                fraction numerator straight x over denominator 5 minus 12 end fraction equals fraction numerator straight y over denominator negative 4 minus 10 end fraction equals space fraction numerator 1 over denominator negative 6 minus 1 end fraction  or  fraction numerator straight x over denominator negative 7 end fraction equals fraction numerator straight y over denominator negative 14 end fraction space equals space fraction numerator 1 over denominator negative 7 end fraction
    therefore space space space space space space space space straight x space equals space fraction numerator negative 7 over denominator negative 7 end fraction space equals space 1 comma space space space space space straight y space equals space fraction numerator negative 14 over denominator negative 7 end fraction space equals space 2
    therefore space space lines space left parenthesis 1 right parenthesis space and space left parenthesis 3 right parenthesis space intersect space in space straight B left parenthesis 1 comma space 2 right parenthesis
    From B. draw BL ⊥ x-axis and from A. draw AM ⊥ x-axis.

    Required area = Area of increment ABC = Area of region BLMA - area of increment BLC space - area of increment ACM
    equals space integral subscript 1 superscript 4 open parentheses fraction numerator straight x plus 5 over denominator 3 end fraction close parentheses dx space minus space integral subscript 1 superscript 2 left parenthesis 4 minus 2 right parenthesis space dx space minus space integral subscript 2 superscript 4 fraction numerator 3 straight x minus 6 over denominator 2 end fraction dx
equals space 1 third integral subscript 1 superscript 4 left parenthesis straight x plus 5 right parenthesis space dx space minus space integral subscript 1 superscript 2 left parenthesis 4 minus 2 straight x right parenthesis space dx space minus 1 half integral subscript 2 superscript 4 left parenthesis 3 straight x minus 6 right parenthesis space dx
equals space 1 third open square brackets straight x squared over 2 plus 5 straight x close square brackets subscript 1 superscript 4 space minus space open square brackets 4 straight x minus straight x squared close square brackets subscript 1 superscript 2 space minus space 1 half open square brackets fraction numerator 3 straight x squared over denominator 2 end fraction minus 6 straight x close square brackets subscript 2 superscript 4
equals space 1 third open square brackets open parentheses 16 over 2 plus 20 close parentheses minus space open parentheses 1 half plus 5 close parentheses close square brackets space minus space left square bracket left parenthesis 8 minus 4 right parenthesis space minus space left parenthesis 4 minus 1 right parenthesis right square bracket minus 1 half left square bracket left parenthesis 24 minus 24 right parenthesis minus left parenthesis 6 minus 12 right parenthesis right square bracket
equals space 1 third open parentheses 28 minus 11 over 2 close parentheses minus left parenthesis 4 minus 3 right parenthesis minus 1 half left parenthesis 0 plus 6 right parenthesis space equals space 1 third cross times 45 over 2 minus 1 minus 3 space equals space 15 over 2 minus 4 space equals 7 over 2 space sq. space units

    Question 44
    CBSEENMA12032734

    Using integration, find the area of the region bounded by (2, 5), (4, 7) and (6, 2).

    Solution

    Let A(2, 5), B(4, 7), C(6, 2) be vertices of ∆ABC. from A, B, C draw AL. BM. CN ⊥ x-axis.
    The equation of AB is
                                straight y minus 5 space equals space fraction numerator 7 minus 5 over denominator 4 minus 2 end fraction left parenthesis straight x minus 2 right parenthesis
    or                    straight y minus 5 space equals 2 over 2 left parenthesis straight x minus 2 right parenthesis
    or                       straight y minus 5 space equals space straight x minus 2
    or                          straight y space equals space straight x plus 3
    The equation of BC is
                       straight y minus 7 space equals space fraction numerator 2 minus 7 over denominator 6 minus 4 end fraction left parenthesis straight x minus 4 right parenthesis space space space space or space space space straight y minus 7 space equals space minus 5 over 2 left parenthesis straight x minus 4 right parenthesis
    or                 straight y minus 7 space equals space minus fraction numerator 5 straight x over denominator 2 end fraction plus 10 space space space space or space space straight y equals negative fraction numerator 5 straight x over denominator 2 end fraction plus 17

    The equation of CA is
                           straight y minus 2 space equals space fraction numerator 5 minus 2 over denominator 2 minus 6 end fraction left parenthesis straight x minus 6 right parenthesis space space space or space straight y minus 2 space equals space minus 3 over 4 left parenthesis straight x minus 6 right parenthesis
    or                     straight y minus 2 space equals space minus fraction numerator 3 straight x over denominator 4 end fraction plus 9 over 2 space space space space space space or space space space space straight y space equals negative fraction numerator 3 straight x over denominator 4 end fraction plus 13 over 2
    Area of increment ABC =  Area ALMB+ area BMNC - area ALNC
                          equals space integral subscript 2 superscript 4 left parenthesis straight x plus 3 right parenthesis space dx plus integral subscript 4 superscript 6 open parentheses negative fraction numerator 5 straight x over denominator 2 end fraction plus 17 close parentheses space dx space minus space integral subscript 2 superscript 6 open parentheses negative fraction numerator 3 straight x over denominator 4 end fraction plus 13 over 2 close parentheses dx
             equals space open square brackets straight x squared over 2 plus 3 straight x close square brackets subscript 2 superscript 4 plus open square brackets fraction numerator negative 5 straight x squared over denominator 4 end fraction plus 17 straight x close square brackets subscript 4 superscript 6 space minus space open square brackets negative fraction numerator 3 straight x squared over denominator 8 end fraction plus fraction numerator 13 space straight x over denominator 2 end fraction close square brackets subscript 2 superscript 6
         equals left parenthesis 8 plus 12 right parenthesis minus left parenthesis 2 plus 6 right parenthesis plus left parenthesis negative 45 plus 102 right parenthesis minus left parenthesis negative 20 plus 68 right parenthesis minus open parentheses negative 27 over 2 plus 39 close parentheses plus open parentheses negative 3 over 2 plus 13 close parentheses
equals 20 minus 8 plus 57 minus 48 minus 51 over 2 plus 23 over 2
equals fraction numerator 40 minus 16 plus 114 minus 96 minus 51 plus 23 over denominator 2 end fraction equals 14 over 2 space equals space 7 space sq. space units. space

    Question 45
    CBSEENMA12032737

    Using the method of integration, find the area of the triangle ABC, co-ordinates of whose vertices are A (2, 0), B (4, 5), C (6, 3).

    Solution

    The equation of AB is
                      straight y minus 0 space space equals space fraction numerator 5 minus 0 over denominator 4 minus 2 end fraction left parenthesis straight x minus 2 right parenthesis
    or               straight y space equals space 5 over 2 left parenthesis straight x minus 2 right parenthesis
    The equation of BC is
                   straight y minus 5 space equals fraction numerator 3 minus 5 over denominator 6 minus 4 end fraction left parenthesis straight x minus 4 right parenthesis
    or             straight y minus 5 space equals space minus left parenthesis straight x minus 4 right parenthesis space space or space space space straight y space equals space minus straight x plus 9
    The equation of CA is
                     straight y minus 3 space equals space fraction numerator 0 minus 3 over denominator 2 minus 6 end fraction left parenthesis straight x minus 6 right parenthesis space space or space straight y minus 3 space equals space 3 over 4 left parenthesis straight x minus 6 right parenthesis space or space space space straight y space equals space fraction numerator 3 straight x over denominator 4 end fraction minus 3 over 2

    From C, draw CD perpendicular x-axis.
    Required area = area of quad. ABCD - area of increment space ADC
                            equals space open square brackets integral subscript 2 superscript 4 5 over 2 left parenthesis straight x minus 2 right parenthesis space dx space plus space integral subscript 4 superscript 6 left parenthesis negative straight x plus 9 right parenthesis space dx close square brackets space minus space integral subscript 2 superscript 6 open parentheses fraction numerator 3 straight x over denominator 4 end fraction minus 3 over 2 close parentheses dx
equals space 5 over 2 open square brackets straight x squared over 2 minus 2 straight x close square brackets subscript 2 superscript 4 space plus open square brackets negative straight x squared over 2 plus 9 straight x close square brackets subscript 4 superscript 6 space minus space open square brackets fraction numerator 3 straight x squared over denominator 8 end fraction minus 3 over 2 straight x close square brackets subscript 2 superscript 6
equals space 5 over 2 open square brackets left parenthesis 8 minus 8 right parenthesis minus left parenthesis 2 minus 4 right parenthesis close square brackets plus open square brackets left parenthesis negative 18 plus 54 right parenthesis minus left parenthesis negative 8 plus 36 right parenthesis close square brackets minus open square brackets open parentheses 27 over 2 minus 9 close parentheses minus open parentheses 3 over 2 minus 3 close parentheses close square brackets
equals space 5 over 2 left parenthesis 0 plus 2 right parenthesis space plus space left parenthesis 36 minus 28 right parenthesis space minus open parentheses 9 over 2 plus 3 over 2 close parentheses
equals space 5 plus 8 minus 6 space equals space 7 space sq. space units.

    Question 46
    CBSEENMA12032739

    Using integration, find the area of the region bounded by the triangle whose vertices are (-1, 1), (0, 5) and (3, 2).

    Solution

    Let A(-1, 1),  B(0, 5), C(3, 2) be the vertices of the given triangle.
    The equation of AB is
             straight y minus 1 space equals space fraction numerator 5 minus 1 over denominator 0 plus 1 end fraction left parenthesis straight x plus 1 right parenthesis comma space space or space space straight y space minus space 1 space equals space 4 space left parenthesis straight x plus 1 right parenthesis
    or   y = 4x + 5                       ...(1)
         The equation of BC is
           straight y minus 5 space equals space fraction numerator 2 minus 5 over denominator 3 minus 0 end fraction left parenthesis straight x minus 0 right parenthesis comma space space space or space straight y space minus 5 space equals space minus left parenthesis straight x minus 0 right parenthesis
 
    or     straight y space equals space minus straight x plus 5                 ...(2)
         The equation of CA is
                   straight y minus 2 space equals space fraction numerator 1 minus 2 over denominator negative 1 minus 3 end fraction left parenthesis straight x minus 3 right parenthesis comma space or space space straight y minus 2 space equals space 1 fourth left parenthesis straight x minus 3 right parenthesis
    or            straight y space equals space straight x over 4 plus 5 over 4
    Required area = Area of ∆ ABC
    = Area of region AMOB + area of region BONC - area of region AMNC
    equals space integral subscript negative 1 end subscript superscript 0 left parenthesis 4 straight x plus 5 right parenthesis space dx space plus space integral subscript 0 superscript 3 left parenthesis negative straight x plus 5 right parenthesis space dx space minus space integral subscript negative 1 end subscript superscript 3 open parentheses straight x over 4 plus 5 over 4 close parentheses space dx
    equals space open square brackets 2 straight x squared plus 5 straight x close square brackets subscript 1 superscript 0 space plus open square brackets negative straight x squared over 2 plus 5 straight x close square brackets subscript 0 superscript 3 space minus space open square brackets straight x squared over 8 plus fraction numerator 5 straight x over denominator 4 end fraction close square brackets subscript negative 1 end subscript superscript 3
equals space open square brackets left parenthesis 0 plus 0 right parenthesis space minus space left parenthesis 2 minus 5 right parenthesis close square brackets space plus space open square brackets open parentheses negative 9 over 2 plus 15 close parentheses minus left parenthesis 0 plus 0 right parenthesis close square brackets space minus space open square brackets open parentheses 9 over 8 plus 15 over 4 close parentheses minus open parentheses 1 over 8 minus 5 over 4 close parentheses close square brackets
equals space 3 plus 21 over 2 minus 39 over 8 minus 9 over 8 space equals space fraction numerator 24 plus 84 minus 39 minus 9 over denominator 8 end fraction equals 60 over 8 equals 15 over 2 equals 7 1 half space sq. space units

    Question 47
    CBSEENMA12032740

    Using integration, find the area of the triangle ABC whose vertices have coordinates A (3, 0), B(4, 6) and C (6, 2).

    Solution

    The given vertices are A (3, 0), B (4, 6), C (6, 2). The equation of AB is
                       straight y minus 0 space equals space fraction numerator 6 minus 0 over denominator 4 minus 3 end fraction left parenthesis straight x minus 3 right parenthesis
    or                   straight y space equals 6 space left parenthesis straight x minus 3 right parenthesis
    or                    straight y space equals space 6 straight x minus 18              ...(1)
    The equation of BC is
                       straight y minus 6 space equals space fraction numerator 2 minus 6 over denominator 6 minus 4 end fraction left parenthesis straight x minus 4 right parenthesis
    or                straight y minus 6 space equals space fraction numerator negative 4 over denominator 2 end fraction left parenthesis straight x minus 4 right parenthesis
    or               straight y minus 6 space equals space minus 2 straight x plus 8
    or                   straight y space equals space minus 2 straight x plus 14            ...(2)
    The equation of CA is
                      straight y minus 2 space equals space fraction numerator 0 minus 2 over denominator 3 minus 6 end fraction left parenthesis straight x minus 6 right parenthesis space space or space space space straight y minus 2 space equals space fraction numerator negative 2 over denominator negative 3 end fraction left parenthesis straight x minus 6 right parenthesis
    or              straight y minus 2 space equals 2 over 3 left parenthesis straight x minus 4 right parenthesis
    or                   straight y space equals 2 over 3 straight x minus 2                 ...(3)
    From B. C draw BM. CN ⊥ s on x-axis.
    Required area = Area of ∆ AMB + Area of trap. MNCB - area of ∆ANC

                            equals space integral subscript 3 superscript 4 left parenthesis 6 straight x minus 18 right parenthesis space dx plus integral subscript 4 superscript 6 left parenthesis negative 2 straight x plus 14 right parenthesis space dx minus integral subscript 3 superscript 6 open parentheses 2 over 3 straight x minus 2 close parentheses space dx
equals space open square brackets 3 straight x squared minus 18 straight x close square brackets subscript 3 superscript 4 space plus space open square brackets negative straight x squared plus 14 straight x close square brackets subscript 4 superscript 6 space minus space open square brackets straight x squared over 3 minus 2 straight x close square brackets subscript 3 superscript 6
equals space left parenthesis 48 minus 72 right parenthesis minus left parenthesis 27 minus 54 right parenthesis plus left parenthesis negative 36 plus 84 right parenthesis minus left parenthesis negative 16 plus 56 right parenthesis minus left parenthesis 12 minus 12 right parenthesis plus left parenthesis 3 minus 6 right parenthesis
equals negative 24 plus 27 plus 48 minus 40 minus 0 minus 3 space equals space 8 space sq. space units. space

    Question 48
    CBSEENMA12032743

    Using integration, find the area of the triangle ABC whose vertices are A (3, 0) B (4, 5) and C (5, 1).

    Solution

    The given vertices are A(3, 0), B(4, 5), C(5, 1).
    The equation of AB is
                       straight y minus 0 space equals fraction numerator 5 minus 0 over denominator 4 minus 3 end fraction left parenthesis straight x minus 3 right parenthesis              
    or              y = 5x - 5  ...(1)

    The equation of BC is
                       straight y minus 5 space equals space fraction numerator 1 minus 5 over denominator 5 minus 4 end fraction left parenthesis straight x minus 4 right parenthesis
    or              
    or               straight y minus 5 space equals space minus 4 straight x space plus 16
    or                  straight y space equals space minus 4 straight x plus 21                                      ...(2)
    The equation of CA is
                       straight y minus 1 space equals fraction numerator 0 minus 1 over denominator 3 minus 5 end fraction left parenthesis straight x minus 5 right parenthesis space space space space or space space space space space straight y space minus 1 space equals space 1 half left parenthesis straight x minus 5 right parenthesis
    or                  straight y minus 1 space equals space straight x over 2 minus 5 over 2          or     straight y space equals straight x over 2 minus 3 over 2               ...(3)
    From B.  C draw BM. CN ⊥s on x-axis
    Required area = Area of ∆AMB + area MNCB — area of ∆ANC
            equals space integral subscript 3 superscript 4 left parenthesis 5 straight x minus 15 right parenthesis space dx space plus space integral subscript 4 superscript 5 left parenthesis negative 4 straight x plus 21 right parenthesis space dx space minus space integral subscript 3 superscript 5 open parentheses straight x over 2 minus 3 over 2 close parentheses dx
equals space open square brackets fraction numerator 5 straight x squared over denominator 2 end fraction minus 15 straight x close square brackets subscript 3 superscript 4 plus open square brackets negative 2 straight x squared plus 21 straight x close square brackets subscript 4 superscript 5 space minus space open square brackets straight x squared over 4 minus 3 over 2 straight x close square brackets subscript 3 superscript 5
equals space left parenthesis 40 minus 60 right parenthesis space minus open parentheses 45 over 2 minus 45 close parentheses plus left parenthesis negative 50 plus 105 right parenthesis minus left parenthesis 32 plus 84 right parenthesis
                                                                             negative open parentheses 25 over 4 minus 15 over 2 close parentheses plus open parentheses 9 over 4 minus 9 over 2 close parentheses
    equals negative 20 plus 45 over 2 plus 55 minus 52 plus 5 over 4 minus 9 over 4 equals negative 17 plus 45 over 2 minus 1 space equals space 9 over 2 space sq. space units.

    Question 49
    CBSEENMA12032744

    Using integration, find the area of the region bounded by the triangle whose vertices are (1, 0), (2, 2) and (3, 1).

    Solution
    Let A (1, 0), B (2, 2), C (3, 1) be the vertices of the given triangle. The equation of AB is
                                       straight y minus 0 space equals space fraction numerator 2 minus 0 over denominator 2 minus 1 end fraction left parenthesis straight x minus 1 right parenthesis comma space space space space or space space straight y space equals space 2 left parenthesis straight x minus 1 right parenthesis space space or space space straight y space equals space 2 straight x minus 2
    The equation of BC is  straight y minus 2 space equals space fraction numerator 1 minus 2 over denominator 3 minus 2 end fraction left parenthesis straight x minus 2 right parenthesis comma space space or space straight y space minus 2 space equals space minus left parenthesis straight x minus 2 right parenthesis
    or    straight y space equals negative straight x plus 4
    Consider straight f left parenthesis straight x right parenthesis space equals space open curly brackets table attributes columnalign left end attributes row cell 2 straight x minus 2 space space if space space 1 less or equal than straight x less or equal than 2 end cell row cell 4 minus straight x space space if space space 2 less or equal than straight x less or equal than 3 end cell end table close

    Let D be the foot of perpendicular from C (3, 1) on x-axis. Therefore, D is (3, 0).
       Area of quad. ABCD = integral subscript 1 superscript 3 straight f left parenthesis straight x right parenthesis space dx
                         equals space integral subscript 1 superscript 2 straight f left parenthesis straight x right parenthesis space dx space plus space integral subscript 2 superscript 3 straight f left parenthesis straight x right parenthesis space dx space equals space integral subscript 1 superscript 2 left parenthesis 2 straight x minus 2 right parenthesis space dx plus integral subscript 2 superscript 3 left parenthesis 4 minus straight x right parenthesis space dx
                           equals space open square brackets straight x squared minus 2 straight x close square brackets subscript 1 superscript 2 plus open square brackets 4 straight x minus straight x squared over 2 close square brackets subscript 2 superscript 3 space equals space open square brackets left parenthesis 4 minus 4 right parenthesis minus space left parenthesis 1 minus 2 right parenthesis close square brackets plus open square brackets open parentheses 12 minus 9 over 2 close parentheses minus left parenthesis 8 minus 2 right parenthesis close square brackets
equals space 0 plus 1 plus 15 over 2 minus 6 space equals space 5 over 2
    The equation of AC is straight y minus 0 space equals space fraction numerator 1 minus 0 over denominator 3 minus 1 end fraction left parenthesis straight x minus 1 right parenthesis
    or     straight y space equals 1 half left parenthesis straight x minus 1 right parenthesis
    Area of increment ACD space equals space integral subscript 1 superscript 3 1 half left parenthesis straight x minus 1 right parenthesis space dx space equals space 1 half open square brackets straight x squared over 2 minus straight x close square brackets subscript 1 superscript 3
                          equals space 1 half open square brackets open parentheses 9 over 2 minus 3 close parentheses minus open parentheses 1 half minus 1 close parentheses close square brackets space equals 1 half open square brackets 3 over 2 plus 1 half close square brackets space equals space 1
    therefore space space space space area space of space increment ABC space equals space Area space of space quad. space ABCD space minus space area space of space increment space ACD
                                       equals space 5 over 2 minus 1 space equals space 3 over 2 sq. space units.

    Question 50
    CBSEENMA12032746

    Using integration find the area of region bounded by the triangle whose vertices are (-1, 0), (1, 3) and (3, 2).

    Solution

    Let A(-1, 0), B(1, 3), C(3, 2) be the vertices of the given triangle. 
    The equation of AB is
                       straight y minus 0 space equals fraction numerator 3 minus 0 over denominator 1 plus 1 end fraction left parenthesis straight x plus 1 right parenthesis
    or                 straight y equals space 3 over 2 left parenthesis straight x plus 1 right parenthesis              ...(1)

    The equation of BC is
                        straight y minus 3 space equals space fraction numerator 2 minus 3 over denominator 3 minus 1 end fraction left parenthesis straight x minus 1 right parenthesis
    or                straight y minus 3 space equals negative 1 half left parenthesis straight x minus 1 right parenthesis space or space straight y minus 3 space equals space minus 1 half straight x plus 1 half
    or                  straight y equals negative 1 half straight x plus 7 over 2                        ...(2)
    The equation of CA is
                      straight y minus 2 space equals space fraction numerator 0 minus 2 over denominator negative 1 minus 3 end fraction left parenthesis straight x minus 3 right parenthesis space space or space space straight y space minus space 2 space equals space 1 half left parenthesis straight x minus 3 right parenthesis
    or         straight y minus 2 space equals space 1 half straight x minus 3 over 2 space space space space or space space space space straight y space equals space 1 half straight x plus 1 half         ...(3)
    From B, draw BM ⊥ x-axis and from C, draw CN ⊥ x-axis.
    Required area = Area of ∆ABC
    = Area of increment AMB + area of region BMNC - area of increment ANC
    equals space integral subscript negative 1 end subscript superscript 1 3 over 2 left parenthesis straight x plus 1 right parenthesis space dx plus integral subscript 1 superscript 3 open parentheses negative 1 half straight x plus 7 over 2 close parentheses dx space minus space integral subscript negative 1 end subscript superscript 3 open parentheses 1 half straight x plus 1 half close parentheses dx
equals space 3 over 2 open square brackets straight x squared over 2 plus straight x close square brackets subscript negative 1 end subscript superscript 1 plus open square brackets negative straight x squared over 4 plus 7 over 2 straight x close square brackets subscript 1 superscript 3 space minus space open square brackets straight x squared over 4 plus straight x over 2 close square brackets subscript negative 1 end subscript superscript 3
equals space 3 over 2 open square brackets open parentheses 1 half plus 1 close parentheses minus open parentheses 1 half minus 1 close parentheses close square brackets plus open square brackets open parentheses negative 9 over 4 plus 21 over 2 close parentheses minus open parentheses negative 1 fourth plus 7 over 2 close parentheses close square brackets minus open square brackets open parentheses 9 over 4 plus 3 over 2 close parentheses minus open parentheses 1 fourth minus 1 half close parentheses close square brackets
    equals space 3 over 2 open parentheses 3 over 2 plus 1 half close parentheses plus open parentheses 33 over 4 minus 13 over 4 close parentheses minus open parentheses 15 over 4 plus 1 fourth close parentheses
equals space 9 over 4 plus 3 over 4 plus 33 over 4 minus 13 over 4 minus 15 over 4 minus 1 fourth equals 16 over 4 space equals space 4 space sq. space units.

    Question 51
    CBSEENMA12032749

    Find the area of the region enclosed between the two circles x2 + y2 = 4 and (x - 2)2 + y2 = 4.

    Solution
    The equations of the given circles are
                               straight x squared plus straight y squared space equals space 4 space space space space space space... left parenthesis 1 right parenthesis
    and                left parenthesis straight x minus 2 right parenthesis squared plus straight y squared space equals space 4  ...(2)
      Equation (1) is a circle with centre O at the origin and radius 2. Equation (2) is a circle with centre C(2, 0) and radius 2.
        Solving equations (1) and (2), we have
                            left parenthesis straight x minus 2 right parenthesis squared plus straight y squared space equals space straight x squared plus straight y squared
    or                 straight x squared minus 4 straight x plus 4 plus straight y squared space equals space straight x squared plus straight y squared
    or                  negative 4 straight x plus 4 space equals space 0 space space space space space space space rightwards double arrow space space space straight x space minus space 1 space equals 0
    or                       x = 1
    therefore   from  (1),      1 plus straight y squared space equals space 4 space space space space or space space straight y squared space equals space 3
    therefore space space space space space space straight y space equals space plus-or-minus square root of 3


    therefore the points of intersection of the given circles are straight A left parenthesis 1 comma space square root of 3 right parenthesis space and space straight A left parenthesis 1 comma space minus square root of 3 right parenthesis end root.
    Required area of the enclosed region OACA'O between the circles
          = 2 [area of region ODCAO]
          =2 [area of region ODAO + area of the region DCAD]
          equals space 2 open square brackets integral subscript 0 superscript 1 straight y space dx space plus space integral subscript 1 superscript 2 straight y space dx close square brackets space equals space 2 open square brackets integral subscript 0 superscript 1 square root of 4 minus left parenthesis straight x minus 2 right parenthesis squared end root space dx space plus integral subscript 1 superscript 2 square root of 4 minus straight x squared end root dx close square brackets
equals space 2 open square brackets 1 half left parenthesis straight x minus 2 right parenthesis space square root of 4 minus left parenthesis straight x minus 2 right parenthesis squared end root plus 1 half cross times 4 space sin to the power of negative 1 end exponent open parentheses fraction numerator straight x minus 2 over denominator 2 end fraction close parentheses close square brackets subscript 0 superscript 1
                                                                               plus 2 space open square brackets 1 half straight x square root of 4 minus straight x squared end root plus 1 half cross times 4 space sin to the power of negative 1 end exponent straight x over 2 close square brackets subscript 1 superscript 2
            equals space open square brackets left parenthesis straight x minus 2 right parenthesis space square root of 4 minus left parenthesis straight x minus 2 right parenthesis squared end root plus 4 space sin to the power of negative 1 end exponent open parentheses fraction numerator straight x minus 2 over denominator 2 end fraction close parentheses close square brackets subscript 0 superscript 1 plus open square brackets straight x square root of 4 minus straight x squared end root plus 4 space sin to the power of negative 1 end exponent straight x over 2 close square brackets subscript 1 superscript 2
equals space open square brackets open parentheses negative square root of 3 plus 4 space sin to the power of negative 1 end exponent open parentheses fraction numerator negative 1 over denominator 2 end fraction close parentheses close parentheses minus 4 space sin to the power of negative 1 end exponent left parenthesis negative 1 right parenthesis close square brackets plus open square brackets 4 space sin to the power of negative 1 end exponent 1 space minus square root of 3 minus 4 space sin to the power of negative 1 end exponent 1 half close square brackets
equals space open square brackets open parentheses negative square root of 3 minus 4 cross times straight pi over 6 close parentheses plus 4 cross times straight pi over 2 close square brackets plus open square brackets 4 cross times straight pi over 2 minus square root of 3 minus 4 cross times straight pi over 6 close square brackets
equals space open parentheses negative square root of 3 minus fraction numerator 2 straight pi over denominator 3 end fraction plus 2 straight pi close parentheses plus open parentheses 2 space straight pi space minus square root of 3 minus fraction numerator 2 straight pi over denominator 3 end fraction close parentheses space equals space fraction numerator 8 straight pi over denominator 3 end fraction minus 2 square root of 3
    Question 52
    CBSEENMA12032753

    Find the area of the region enclosed between the two circles  x2 + y2 = 1 and (x - 1)2 + y2 = 1. 

    Solution

    The equation of two circles are
                            straight x squared plus straight y squared space equals space 1                          ...(1)
       and         left parenthesis straight x minus 1 right parenthesis squared plus straight y squared space equals space 1                       ...(2)
    Centre of circle (1) is O (0, 0) and radius OA = 1
    Centre of circle (2) is A (1, 0) and radius AO = 1
    Subtracting (1) from (2), we get,
    negative 2 straight x plus 1 space equals space 0 space space space space space space rightwards double arrow space space space space straight x space equals space 1 half
    Putting straight x space equals space 1 half in (1), we get,
                     1 fourth plus straight y squared space equals space 1 space space space space space space rightwards double arrow space space space space straight y squared equals space 3 over 4
    rightwards double arrow space space space space space straight y space equals space plus-or-minus fraction numerator square root of 3 over denominator 2 end fraction


    therefore     points of intersection of circles (1) and (2) are
                      straight P open parentheses 1 half comma space fraction numerator square root of 3 over denominator 2 end fraction close parentheses space space and space straight Q space open parentheses 1 half comma space minus fraction numerator square root of 3 over denominator 2 end fraction close parentheses
            Required area =  Area of region OQAP
                          = 2 (area of region OMAP)
                         = 2 (area of region OMPO + area  of region MAPM)
                          equals space 2 open square brackets integral subscript 0 superscript 1 divided by 2 end superscript square root of 1 minus left parenthesis straight x minus 1 right parenthesis squared end root dx plus integral subscript 1 divided by 2 end subscript superscript 1 square root of 1 minus straight x squared end root close square brackets
                           equals space 2 open square brackets fraction numerator left parenthesis straight x minus 1 right parenthesis thin space square root of 1 minus left parenthesis straight x minus 1 right parenthesis squared end root over denominator 2 end fraction plus 1 half sin to the power of negative 1 end exponent left parenthesis straight x minus 1 right parenthesis close square brackets subscript 0 superscript 1 half end superscript plus 2 open square brackets fraction numerator straight x square root of 1 minus straight x squared end root over denominator 2 end fraction plus 1 half sin to the power of negative 1 end exponent straight x close square brackets subscript 1 half end subscript superscript 1
                           equals space 2 open square brackets open curly brackets fraction numerator open parentheses begin display style 1 half end style minus 1 close parentheses square root of 1 minus open parentheses begin display style 1 half end style minus 1 close parentheses squared end root over denominator 2 end fraction plus 1 half sin to the power of negative 1 end exponent open parentheses 1 half minus 1 close parentheses close curly brackets close square brackets
    negative open curly brackets fraction numerator left parenthesis 0 minus 1 right parenthesis space square root of 1 minus left parenthesis 0 minus 1 right parenthesis squared end root over denominator 2 end fraction plus 1 half sin to the power of negative 1 end exponent left parenthesis 0 minus 1 right parenthesis close curly brackets plus 2 space open square brackets open parentheses 0 plus 1 half sin to the power of negative 1 end exponent 1 close parentheses minus fraction numerator begin display style 1 half end style square root of 1 minus begin display style 1 fourth end style end root over denominator 2 end fraction plus 1 half sin to the power of negative 1 end exponent open parentheses 1 half close parentheses close square brackets
                   equals space 2 open square brackets fraction numerator negative begin display style 1 half end style cross times begin display style fraction numerator square root of 3 over denominator 2 end fraction end style over denominator 2 end fraction plus 1 half sin to the power of negative 1 end exponent open parentheses negative 1 half close parentheses minus 0 minus 1 half sin to the power of negative 1 end exponent left parenthesis negative 1 right parenthesis close square brackets
                                                                                                     plus space 2 space open square brackets 1 half sin to the power of negative 1 end exponent 1 minus fraction numerator begin display style 1 half end style cross times begin display style fraction numerator square root of 3 over denominator 2 end fraction end style over denominator 2 end fraction minus 1 half sin to the power of negative 1 end exponent 1 half close square brackets
        equals space minus fraction numerator square root of 3 over denominator 4 end fraction plus open parentheses negative straight pi over 6 close parentheses minus open parentheses negative straight pi over 2 close parentheses plus straight pi over 2 minus fraction numerator square root of 3 over denominator 4 end fraction minus straight pi over 6
equals space open parentheses negative straight pi over 6 plus straight pi over 2 plus straight pi over 2 minus straight pi over 6 close parentheses minus 2 cross times fraction numerator square root of 3 over denominator 4 end fraction space equals space open parentheses 2 straight pi over 3 minus fraction numerator square root of 3 over denominator 2 end fraction close parentheses space sq. space units.
                       

    Question 53
    CBSEENMA12032756

    Find the area of the region enclosed between the two circles x2 + y2 = 1 and open parentheses straight x minus 1 half close parentheses squared plus straight y squared space equals space 1.

    Solution
    The equations of two circles are
    x2 + y2 = 1    ...(1)
    and open parentheses straight x minus 1 half close parentheses squared plus straight y squared space equals space 1    ...(2)
    Centre of circle (1) is O(0, 0) and radius OA = 1
     Centre of circle (2) is straight B open parentheses 1 half comma space 0 close parentheses and radius CB = 1
    Subtraction (1) from (2), we get,
                          negative straight x plus 1 fourth space equals space 0 space space space space space rightwards double arrow space space space straight x space equals space 1 fourth
    Putting straight x space equals space 1 fourth in (1), we get,
                          1 over 16 plus straight y squared space equals space 1 space space or space space straight y squared space equals space 15 over 16 space space space space rightwards double arrow space space space space straight y space equals space plus-or-minus fraction numerator square root of 15 over denominator 4 end fraction
    therefore points of intersection of circles (1) and (2) are straight P open parentheses 1 fourth comma space fraction numerator square root of 15 over denominator 4 end fraction close parentheses and straight Q space open parentheses 1 fourth comma space minus fraction numerator square root of 15 over denominator 2 end fraction close parentheses
    Required area = Area of region APCQA
                   = 2[area of region APCA] = [area of region CMPC + area of region MAPM]
                      
    equals space 2 open square brackets integral subscript negative 1 divided by 2 end subscript superscript 1 divided by 4 end superscript square root of 1 minus open parentheses straight x minus 1 half close parentheses squared end root dx space plus space integral subscript 1 divided by 4 end subscript superscript 1 space square root of 1 minus straight x squared end root dx close square brackets
    equals space 2 open square brackets fraction numerator open parentheses straight x minus begin display style 1 half end style close parentheses space square root of 1 minus open parentheses straight x minus begin display style 1 half end style close parentheses squared end root over denominator 2 end fraction plus 1 half sin to the power of negative 1 end exponent open parentheses straight x minus 1 half close parentheses close square brackets subscript fraction numerator negative 1 over denominator 2 end fraction end subscript superscript 1 fourth end superscript plus 2 open square brackets fraction numerator straight x square root of 1 minus straight x squared end root over denominator 2 end fraction plus 1 half sin to the power of negative 1 end exponent straight x close square brackets subscript 1 fourth end subscript superscript 1
    equals space open square brackets open parentheses straight x minus 1 half close parentheses square root of 1 minus open parentheses straight x minus 1 half close parentheses squared end root plus sin to the power of negative 1 end exponent open parentheses straight x minus 1 half close parentheses close square brackets subscript negative 1 half end subscript superscript 1 fourth end superscript plus open square brackets straight x square root of 1 minus straight x squared end root plus sin to the power of negative 1 end exponent straight x close square brackets subscript 1 fourth end subscript superscript 1
equals space open square brackets open curly brackets negative 1 fourth square root of 1 minus 1 over 16 end root plus sin to the power of negative 1 end exponent open parentheses negative 1 fourth close parentheses close curly brackets minus open curly brackets 0 plus sin to the power of negative 1 end exponent left parenthesis negative 1 right parenthesis close curly brackets close square brackets
                                                                                  plus open square brackets left parenthesis 0 plus sin to the power of negative 1 end exponent 1 right parenthesis space minus space open parentheses 1 fourth fraction numerator square root of 15 over denominator 4 end fraction plus sin to the power of negative 1 end exponent 1 fourth close parentheses close square brackets
    equals space open square brackets negative 1 fourth cross times fraction numerator square root of 15 over denominator 4 end fraction minus sin to the power of negative 1 end exponent 1 fourth minus open parentheses negative straight pi over 2 close parentheses close square brackets plus open square brackets straight pi over 2 minus fraction numerator square root of 15 over denominator 16 end fraction minus sin to the power of negative 1 end exponent 1 fourth close square brackets
equals space open parentheses negative fraction numerator square root of 15 over denominator 16 end fraction minus sin to the power of negative 1 end exponent 1 fourth plus straight pi over 2 close parentheses plus open parentheses negative fraction numerator square root of 15 over denominator 16 end fraction minus sin to the power of negative 1 end exponent 1 fourth plus straight pi over 2 close parentheses space equals 2 open parentheses negative fraction numerator square root of 15 over denominator 16 end fraction minus sin to the power of negative 1 end exponent 1 fourth plus straight pi over 2 close parentheses
equals space open parentheses negative fraction numerator square root of 15 over denominator 8 end fraction minus 2 space sin to the power of negative 1 end exponent 1 fourth plus straight pi close parentheses space sq. space units. space
    Question 54
    CBSEENMA12032758

    Find the area of the region bounded by two parabola 4 y = x2 and 4 x = y2

    Solution

    The equations of curves are
                              straight y squared space equals space 4 straight x                                             ...(1)
    and                    straight x squared space equals space 4 straight y                                             ...(2)
    From (2),      straight y space equals space straight x squared over 4                                                  ...(3)
                 Putting this value of y in (1),
                         straight x to the power of 4 over 16 space equals space 4 space straight x space space space space or space space space straight x to the power of 4 space equals space 64 space straight x
    or          straight x left parenthesis straight x cubed minus 64 right parenthesis space equals space 0
    therefore space space space straight x space equals space 0 comma space space 4
therefore space space space from space left parenthesis 3 right parenthesis comma space space space straight y space equals space 0 comma space space 4
because space space space curves space left parenthesis 1 right parenthesis space and space left parenthesis 2 right parenthesis space intersect space in space straight O left parenthesis 0 comma space 0 right parenthesis comma space straight P space left parenthesis 4 comma space 4 right parenthesis.



                    From P, draw PM perpendicular x-axis. 
                    Required area = Area OAPB
                                           = Area OBPM - area OAPM
                          equals space integral subscript 0 superscript 4 4 square root of straight x space dx space space minus integral subscript 0 superscript 4 straight x squared over 4 dx space equals space 2 integral subscript 0 superscript 4 straight x to the power of 1 half end exponent dx minus 1 fourth integral subscript 0 superscript 4 straight x squared space dx space equals space 2 space open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript 4 space minus space 1 fourth open square brackets straight x cubed over 3 close square brackets subscript 0 superscript 4
equals space 2 space cross times 2 over 3 open square brackets straight x to the power of 3 over 2 end exponent close square brackets subscript 0 superscript 4 space minus space 1 fourth cross times 1 third open square brackets straight x cubed close square brackets subscript 0 superscript 4 space equals space 4 over 3 open square brackets left parenthesis 4 right parenthesis to the power of 3 over 2 end exponent minus 0 close square brackets minus 1 over 12 left square bracket left parenthesis 4 right parenthesis cubed minus 0 right square bracket
equals space 4 over 3 cross times 8 minus 1 over 12 cross times 64 space equals space 32 over 3 minus 16 over 3 equals space 16 over 3 space sq. space units. space

    Question 55
    CBSEENMA12032760

    Find the area included between the two curves y2 = 9x and ,x2 = 9y. Also draw the rough sketch.

    Solution

    The equations of curves are
                               straight y squared space equals 9 straight x                                             ...(1)
        and                 straight x squared space equals space 9 straight y                                            ...(2)
        From (1) and (2), we get
                    open parentheses straight x squared over 9 close parentheses squared space equals space 9 space straight x space space space space space space space space or space space space space space space straight x to the power of 4 over 81 space equals space 9 straight x
    therefore space space space straight x to the power of 4 minus 729 straight x space equals space 0 space space space space space space space space space rightwards double arrow space space straight x left parenthesis straight x cubed minus 729 right parenthesis space equals space 0
therefore space space straight x space equals space 0 comma space space 9
therefore space space straight y space equals space 0 comma space 9

    therefore   curves (1) and (2) intersect in O(0, 0), P(9, 9)
          From P, draw PM space perpendicular x-axis. 
          Required area = Area OAPBO = Area OBPM - area OAPM
                                  equals space integral subscript 0 superscript 9 square root of 9 straight x end root space dx space minus space integral subscript 0 superscript 9 straight x squared over 9 dx space equals space 3 integral subscript 0 superscript 9 straight x to the power of 1 half end exponent dx minus 1 over 9 integral subscript 0 superscript 9 straight x squared dx
        equals space 3 space open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript 9 space minus space 1 over 9 open square brackets straight x cubed over 3 close square brackets subscript 0 superscript 9 space equals space 2 space open square brackets straight x to the power of 3 over 2 end exponent close square brackets subscript 0 superscript 9 space minus space 1 over 27 open square brackets straight x cubed close square brackets subscript 0 superscript 9
equals space 2 space open square brackets 9 to the power of 3 over 2 end exponent minus 0 close square brackets space minus space 1 over 27 open square brackets 9 cubed minus 0 close square brackets
equals space 2 space left parenthesis 27 minus 0 right parenthesis space minus space 1 over 27 left parenthesis 729 minus 0 right parenthesis
equals space 54 minus 27 space equals space 27 space sq. space units. space

    Question 56
    CBSEENMA12032762

    Calculate the area of the region bounded by the y = x2 and x = y2.

    Solution
    The equations of parabolas are
                   straight y squared space equals space straight x                                ...(1)
    and       straight x squared space equals space straight y                                  ...(2)
    From (2), straight y equals straight x squared                               ....(3)
    Putting this values of y in (1), we get,
                             straight x to the power of 4 space equals space straight x space space space or space space space straight x left parenthesis straight x cubed minus 1 right parenthesis space equals space 0
    rightwards double arrow space space space straight x space equals space 0 comma space 1
    therefore space space space space from space left parenthesis 3 right parenthesis comma space space straight y space equals space 0 comma space space space 1
therefore space space space space parabolas space left parenthesis 1 right parenthesis space and space left parenthesis 2 right parenthesis space intersect space in space straight O left parenthesis 0 comma space 0 right parenthesis comma space straight P left parenthesis 1 comma space 1 right parenthesis.

    From P draw PM perpendicular x-axis
    Required area = Area of region OAPB = Area of region OBPM - area of region OAPM
                           equals integral subscript 0 superscript 1 square root of straight x space dx space minus space integral subscript 0 superscript 1 straight x squared dx
                         equals space open square brackets fraction numerator straight x to the power of 3 divided by 2 end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript 1 space minus space open square brackets straight x cubed over 3 close square brackets subscript 0 superscript 1 space equals space 2 over 3 open square brackets straight x to the power of 3 divided by 2 end exponent close square brackets subscript 0 superscript 1 space minus space 1 third open square brackets straight x cubed close square brackets subscript 0 superscript 1
equals space 2 over 3 left square bracket 1 minus 0 right square bracket space minus 1 third left square bracket 1 minus 0 right square bracket space equals space 2 over 3 minus 1 third space equals space 1 third space sq. space units.
     
    Question 57
    CBSEENMA12032765

    Draw a graph of y2 = 16 x and x2 = 16y, and evaluate the area between them.

    Solution
    The equations of curves are
                                                straight y squared space equals space 16 space straight x                        ...(1)
    and                                     straight x squared space equals 16 space straight y                          ...(2)
    From (2),                   straight y space equals space straight x squared over 16                                     ...(3)
    Putting this value of y in (1), we get,
                              straight x to the power of 4 over 256 space equals space 16 space straight x space space space space or space space space straight x to the power of 4 space equals space 4096
    or              straight x space left parenthesis straight x cubed minus 4096 right parenthesis space equals space 0
    therefore space space space space space space space space space space space straight x space equals space 0 comma space space space 16
    therefore space space space from space space left parenthesis 3 right parenthesis comma space space straight y space equals 0 comma space space 16
therefore space space space space curves space left parenthesis 1 right parenthesis space and space left parenthesis 2 right parenthesis space intersect space in
             O(0, 0),  P(16, 16)
    From P, draw PM perpendicular space straight x minus axis.

    Required area = Area OAPB = Area OBPM - area OAPM
                           equals space integral subscript 0 superscript 16 square root of 16 space straight x end root dx space space minus integral subscript 0 superscript 16 straight x squared over 16 dx space equals space 4 integral subscript 0 superscript 16 straight x to the power of 1 half end exponent dx space minus space 1 over 16 integral subscript 0 superscript 16 straight x squared space dx
equals space 4 open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript 16 space minus space 1 over 16 open square brackets straight x cubed over 3 close square brackets subscript 0 superscript 16
equals space 8 over 3 open square brackets left parenthesis 16 right parenthesis to the power of 3 over 2 end exponent minus 0 close square brackets minus 1 over 48 left square bracket left parenthesis 16 right parenthesis cubed minus 0 right square bracket
equals space 8 over 3 cross times 64 minus 1 over 48 cross times 4096 space equals space 512 over 3 minus 256 over 3 space equals space 256 over 3 space sq. space units. space
    Question 58
    CBSEENMA12032767

    Find the area of the region included between the parabolas y2 = 4 a x and x2 = 4 a y, a > 0.    

    Solution

    The equations of curves are
                       straight y squared space equals space 4 space straight a space straight x                   ...(1)
    and             straight x squared space equals 4 space straight a space straight y                   ...(2)
    From (2), straight y equals fraction numerator straight x squared over denominator 4 space straight a end fraction                          ...(3)
    Putting this value of y in (1),
    fraction numerator straight x to the power of 4 over denominator 16 space straight a squared end fraction space equals space 4 space straight a space straight x comma space space or space space space straight x to the power of 4 space equals space 64 space straight a cubed space straight x
    or                straight x left parenthesis straight x cubed minus 64 straight a cubed right parenthesis space equals 0
    ∴ x = 0, 4 a
    ∴ from (3), y = 0, 4 a
    ∴ curves (1) and (2) intersect in O (0, 0), P (4 a, 4 a).
    From P. draw PM ⊥ x-axis.
    Required area = Area OAPB
    = Area OBPM - area OAPM
    equals space integral subscript straight a superscript 4 straight a end superscript square root of 4 space straight a space straight x end root space dx space minus space integral subscript 0 superscript 4 straight a end superscript fraction numerator straight x squared over denominator 4 straight a end fraction dx space equals space 2 square root of straight a integral subscript 0 superscript 4 space straight a space end superscript straight x to the power of 1 half end exponent dx space minus space fraction numerator 1 over denominator 4 space straight a end fraction integral subscript 0 superscript 4 space straight a end superscript straight x squared space dx
     equals space 2 square root of straight a open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript 4 straight a end superscript space minus space fraction numerator 1 over denominator 4 straight a end fraction open square brackets straight x cubed over 3 close square brackets subscript 0 superscript 4 straight a end superscript
equals space 2 square root of straight a cross times 2 over 3 open square brackets straight x to the power of 3 over 2 end exponent close square brackets subscript 0 superscript 4 straight a end superscript space minus space fraction numerator 1 over denominator space 4 straight a end fraction cross times 1 third open square brackets straight x cubed close square brackets subscript 0 superscript 4 straight a end superscript
equals space fraction numerator 4 square root of straight a over denominator 3 end fraction open square brackets left parenthesis 4 space straight a right parenthesis to the power of 3 over 2 end exponent minus 0 close square brackets space minus space fraction numerator 1 over denominator 12 space straight a end fraction open square brackets left parenthesis 4 space straight a right parenthesis cubed space minus space 0 close square brackets
equals space fraction numerator 4 square root of straight a over denominator 3 end fraction cross times 8 straight a to the power of 3 over 2 end exponent minus fraction numerator 1 over denominator 12 space straight a end fraction cross times 64 space straight a cubed space equals space 32 over 3 straight a squared minus 16 over 3 straight a squared space equals space 16 over 3 straight a squared space sq. space units.

    Question 59
    CBSEENMA12032768

    Draw the rough sketch of y2 = x + 1 and y2 = - x + 1 and determine the area enclosed by the two curves.

    Solution

     The equation of given curves are
    y2 - x + 1    ...(1)
    and    y2 = -x + 1    ...(2)
    From (1) and (2), we get,
    x + 1 = -x + 1 ⇒ 2 x = 0 ⇒ x = 0
    Putting x = 0 in (1). we get,
    y2 = 1 or y = -1, 1
    ∴ points of intersection of given curves are (0, -1) and (0, 1).
    Now (1) and (2) represent two parabolas having vertices at (-1, 0) and (1, 0).
    Required area = 2 [area CAO + area OBC]
                           equals space 2 open square brackets integral subscript negative 1 end subscript superscript 0 square root of straight x plus 1 end root dx plus integral subscript 0 superscript 1 square root of straight x minus 1 end root dx close square brackets
      equals space 2 space open square brackets fraction numerator left parenthesis straight x plus 1 right parenthesis to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript negative 1 end subscript superscript 0 plus 2 open square brackets fraction numerator left parenthesis 1 minus straight x right parenthesis to the power of begin display style 3 over 2 end style end exponent over denominator negative begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript 1
equals space 4 over 3 open square brackets open parentheses straight x plus 1 close parentheses to the power of 3 over 2 end exponent close square brackets subscript negative 1 end subscript superscript 0 space minus space 4 over 3 open square brackets left parenthesis 1 minus straight x right parenthesis to the power of 3 over 2 end exponent close square brackets subscript 0 superscript 1
equals space 4 over 3 left square bracket left parenthesis 1 minus 0 right parenthesis right square bracket space minus 4 over 3 open square brackets 0 minus 1 to the power of 3 over 2 end exponent close square brackets
space equals space 4 over 3 plus 4 over 3 space equals space 8 over 3 space sq. space units. space 


    Question 60
    CBSEENMA12032769

    Find the area of the region
    {(x, y): 0 ≤ y ≤ x2 + 1 , 0 ≤ y ≤ x + 1, 0 ≤ x ≤ 2}.

    Solution

     The given region is
    {( x, y): 0 ≤ y ≤ x2 + 1, 0 ≤ y ≤ x + 1, 0 ≤ x ≤ 2}
    Thus region is the intersection of the following regions:
    R1 = {(x, y) : 0 ≤ y ≤ x2 + 1}
    R2 = { (x, y) : 0 ≤ y ≤ x + 1}
    R3 = {(x, y) : 0 ≤ x ≤ 2}
    The function with graph in the figure is
    straight f left parenthesis straight x right parenthesis space equals space open curly brackets table attributes columnalign left end attributes row cell straight x squared plus 1 space space space space if space space space 0 space less or equal than space straight x space less or equal than space 1 end cell row cell straight x plus 1 space space space space space space if space space space 1 space less or equal than space straight x space less or equal than space 2 end cell end table close
    Consider the equations
    y = x2 + 1    ...(1)
    and y = x + 1    ...(2)
    Putting y = x + 1 in (1), we get
    x + 1 = x2 + 1, or x = x2 ⇒ x2 - x = 0 ⇒ x(x - 1) = 0
    ∴ x = 0, 1
    ∴ from (2), y = 1, 2
    ∴ curve (1) and (2) intersect in the points P (0, 1) and Q (1, 2).
    The region considered is bounded by
                                  y = f(x),
                                  y = 0
                                  x = 0
                  and          x = 2
    therefore required area = integral subscript 0 superscript 2 straight f left parenthesis straight x right parenthesis space dx
                                equals space integral subscript 0 superscript 1 straight f left parenthesis straight x right parenthesis space dx plus integral subscript 1 superscript 2 straight f left parenthesis straight x right parenthesis space dx space equals space integral subscript 0 superscript 1 left parenthesis straight x squared plus 1 right parenthesis dx plus integral subscript 1 superscript 2 left parenthesis straight x plus 1 right parenthesis space dx
equals space open square brackets straight x cubed over 3 plus straight x close square brackets subscript 0 superscript 1 plus open square brackets straight x squared over 2 plus straight x close square brackets subscript 1 superscript 2
equals space open square brackets open parentheses 1 third plus 1 close parentheses minus left parenthesis 0 plus 0 right parenthesis close square brackets space plus space open square brackets left parenthesis 2 plus 2 right parenthesis space minus space open parentheses 1 half plus 1 close parentheses close square brackets
equals space 4 over 3 minus 0 plus 4 minus 3 over 2 equals space 16 over 3 minus 3 over 2 equals fraction numerator 32 minus 9 over denominator 6 end fraction equals 23 over 6 space sq. space units. space

    Question 61
    CBSEENMA12032771

    Find the area of the region {(x, y): x2 + y2 ≤ 1 ≤ x + y}.

    Solution

    The given region is
                      open curly brackets open parentheses straight x comma space straight y close parentheses colon straight x squared plus straight y squared less or equal than 1 less or equal than straight x plus straight y close curly brackets
    Consider the equations
                        straight x squared plus straight y squared space equals 1                             ...(1)
               and   x + y = 1                                   ...(2)
    From (2),  y = 1 - x                                      ...(3)

    Putting this value of y in (1), we get,
                       straight x squared plus left parenthesis 1 minus straight x right parenthesis squared space equals space 1 space space space rightwards double arrow space space 2 straight x squared minus 2 straight x space equals space 0
    rightwards double arrow                         straight x squared minus straight x space equals 0 space space space rightwards double arrow space space straight x left parenthesis straight x minus 1 right parenthesis space equals space 0 space space space rightwards double arrow space space straight x space equals space 0 comma space space 1
    therefore space space space from space left parenthesis 3 right parenthesis comma space space straight y space equals space 1 minus 0 comma space space 1 minus 1 space equals space 1 comma space space 0
therefore space space space circle space left parenthesis 1 right parenthesis space and space st. space line space straight x space plus space straight y space equals space 1 space space intersect space in space the space points space straight A thin space left parenthesis 1 comma space 0 right parenthesis space and space straight B left parenthesis 0 comma space 1 right parenthesis.
    Required area = Area of shaded region  = integral subscript 0 superscript 1 square root of 1 minus straight x squared end root space dx space space minus space integral subscript 0 superscript 1 left parenthesis 1 minus straight x right parenthesis space dx
                          equals space open square brackets fraction numerator straight x square root of 1 minus straight x squared end root over denominator 2 end fraction plus 1 half sin to the power of negative 1 end exponent straight x close square brackets subscript 0 superscript 1 space minus space open square brackets straight x minus straight x squared over 2 close square brackets subscript 0 superscript 1
equals space open square brackets open parentheses 0 plus 1 half sin to the power of negative 1 end exponent straight x close parentheses space open parentheses 0 plus 1 half sin to the power of negative 1 end exponent 0 close parentheses close square brackets space minus open square brackets open parentheses 1 minus 1 half close parentheses minus left parenthesis 0 minus 0 right parenthesis close square brackets
equals space 1 half open parentheses straight pi over 2 close parentheses minus 1 half space equals open parentheses straight pi over 4 minus 1 half close parentheses space sq. space units. space
        

    Question 62
    CBSEENMA12032774

    Find the area of the region bounded by the circle x2 + y2 = 1 and x + y = 1. Also draw a rough sketch.

    Solution

    Consider the equations
                    straight x squared plus straight y squared space equals space 1                               ...(1)
    and         straight x plus straight y space equals space 1                                    ...(2)
    From (2), y = 1 - x                                       ...(3)
    Putting this value of y in (1), we get, 
                   straight x squared plus left parenthesis 1 minus straight x right parenthesis squared space equals space 1 space space space space space space space rightwards double arrow space space space 2 space straight x squared minus 2 straight x space equals space 0
    rightwards double arrow space space space space space straight x squared minus straight x space equals space 0 space space space space space space space rightwards double arrow space space space straight x left parenthesis straight x minus 1 right parenthesis space equals space 0 space space space space rightwards double arrow space space straight x space equals space 0 comma space space 1
therefore space space space from space left parenthesis 3 right parenthesis comma space space straight y space equals space 1 minus 0 comma space space space 1 minus 1 space equals space 1 comma space 0

    therefore circle (1) and st . line x + y = 1 intersect in the points A(1, 0) and B(0, 1).
    Required area = Area of shaded region = integral subscript 0 superscript 1 square root of 1 minus straight x squared end root dx space minus integral subscript 0 superscript 1 left parenthesis 1 minus straight x right parenthesis space dx
                                          equals space open square brackets fraction numerator straight x square root of 1 minus straight x squared end root over denominator 2 end fraction plus 1 half sin to the power of negative 1 end exponent straight x close square brackets subscript 0 superscript 1 space minus space open square brackets straight x minus straight x squared over 2 close square brackets subscript 0 superscript 1
equals space open square brackets open parentheses 0 plus 1 half sin to the power of negative 1 end exponent 1 close parentheses minus open parentheses 0 plus 1 half sin to the power of negative 1 end exponent 0 close parentheses close square brackets space minus space open square brackets open parentheses 1 minus 1 half close parentheses minus left parenthesis 0 minus 0 right parenthesis close square brackets
equals space 1 half open parentheses straight pi over 2 close parentheses minus 1 half space equals open parentheses straight pi over 4 minus 1 half close parentheses space sq. space units. space
               

    Question 63
    CBSEENMA12032776

    Find the area of the region {(x, y): x2 ≤ y ≤ |x|}.
    Or
    Find the area of the region bounded by the parabola y = x2 and y = |x|.

    Solution

    The given region is
          open curly brackets left parenthesis straight x comma space straight y right parenthesis space colon space straight x squared space less or equal than straight y less or equal than open vertical bar straight x close vertical bar close curly brackets
    This region is the intersection of the following regions
                            straight R subscript 1 space equals space open curly brackets left parenthesis straight x comma space straight y right parenthesis space colon space straight x squared space less or equal than space straight y close curly brackets
straight R subscript 2 space equals open curly brackets open parentheses straight x comma space straight y close parentheses colon space straight y space less or equal than open vertical bar straight x close vertical bar close curly brackets
    Consider the equations
                              straight y equals straight x squared                                            ...(1)
                              y = x                                               ...(2)
                       and  y = -x                                            ...(3)

    From (1) and (2), we get
                            straight x equals straight x squared space space space space space space space space space rightwards double arrow space space space straight x squared minus straight x space equals space 0 space space space space space space space space rightwards double arrow space space space straight x left parenthesis straight x minus 1 right parenthesis space space space space space space rightwards double arrow space space space space space straight x space equals space 0 comma space space 1
      from (2), y = 0,  1
    ∴   curve (1) and (2) intersect in the points O (0, 0) and A (1, 1).
    Similarly, curves (1) and (3) intersect in the points O (0, 0) and B (-1, 1)
    Required area = area of shaded region = 2 (area of region OAO)
    equals 2 open square brackets integral subscript 0 superscript 1 straight x space dx minus integral subscript 0 superscript 1 straight x squared space dx close square brackets space equals space 2 space open curly brackets open square brackets straight x squared over 2 close square brackets subscript 0 superscript 1 minus open square brackets straight x cubed over 3 close square brackets subscript 0 superscript 1 close curly brackets
equals space 2 open curly brackets open parentheses 1 half minus 0 close parentheses minus open parentheses 1 third minus 0 close parentheses close curly brackets space equals 2 open parentheses 1 half minus 1 third close parentheses space equals space 2 cross times 1 over 6 equals 1 third space sq space. units.

    Question 64
    CBSEENMA12032779

    Draw the rough sketch and find the area of the region:
    {(x, y) : y2 ≤ 8 x, x2 + x2 ≤ 9} 

    Solution

    Given region is
    {(x, y): y2 ≤ 8 x, x2 +y2 ≤ 9}
    Consider the equations
    y2 = 8 x    ...(1)
    and x2 + y2 = 9    ...(2)
    From (1) and (2). we get,
    x2 + 8 x = 9 or x2 + 8 x-9 = 0⇒ (x + 9)(x - 1) = 0
    ⇒    x = - 9, 1
    which gives the abscissa of the points of intersection P and Q.
    Rejecting negative value of x, we get, x = 1
    Required area = Area of shaded region
                           = 2 (area of region APOA)
                           = 2[area of region AMPA + area of region MOPM]
                           equals space 2 open square brackets integral subscript 0 superscript 1 2 square root of 2 square root of straight x dx plus integral subscript 1 superscript 3 square root of 9 minus straight x squared end root dx close square brackets
equals space 4 square root of 2 integral subscript 0 superscript 1 straight x to the power of 1 half end exponent dx plus 2 integral subscript 1 superscript 3 square root of left parenthesis 3 right parenthesis squared minus straight x squared end root space dx
space equals space 4 square root of 2 open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript 1 plus 2 open square brackets fraction numerator straight x square root of left parenthesis 3 right parenthesis squared minus straight x squared end root over denominator 2 end fraction plus fraction numerator left parenthesis 3 right parenthesis squared over denominator 2 end fraction sin to the power of negative 1 end exponent open parentheses straight x over 3 close parentheses close square brackets subscript 1 superscript 3
equals space fraction numerator 8 square root of 2 over denominator 3 end fraction open square brackets straight x to the power of 3 over 2 end exponent close square brackets subscript 0 superscript 1 plus space open square brackets straight x square root of 9 minus straight x squared end root plus 9 space s i n to the power of negative 1 end exponent open parentheses straight x over 3 close parentheses close square brackets subscript 1 superscript 3
equals space fraction numerator 8 square root of 2 over denominator 3 end fraction left parenthesis 1 minus 0 right parenthesis plus open parentheses 3 square root of 9 minus 9 end root plus 9 space sin to the power of negative 1 end exponent 1 close parentheses minus open parentheses 1 square root of 9 minus 1 end root plus 9 space sin to the power of negative 1 end exponent 1 third close parentheses
equals space fraction numerator 8 square root of 2 over denominator 3 end fraction plus open parentheses 0 plus 9 cross times straight pi over 2 close parentheses minus open parentheses square root of 8 plus 9 space sin to the power of negative 1 end exponent 1 third close parentheses
equals space fraction numerator 8 square root of 2 over denominator 3 end fraction plus fraction numerator 9 straight pi over denominator 2 end fraction minus 2 square root of 2 minus 9 space sin to the power of negative 1 end exponent open parentheses 1 third close parentheses
equals space open square brackets fraction numerator 2 square root of 2 over denominator 3 end fraction plus fraction numerator 9 straight pi over denominator 2 end fraction minus 9 space sin to the power of negative 1 end exponent open parentheses 1 third close parentheses close square brackets space sq. space units.

    Question 65
    CBSEENMA12032784

    Find the area of the region {(x, y): y2 ≤ 4 x, 4x2 + 4 y2 ≤ 9}

    Solution

    Given region is
                        open curly brackets left parenthesis straight x comma space straight y right parenthesis space colon space straight y squared space less or equal than space 4 space straight x comma space space 4 straight x squared plus 4 straight y squared less or equal than 9 close curly brackets
    Consider the equations
                             straight y squared space equals 4 space straight x                                                       ...(1)
    and               4 straight x squared plus 4 straight y squared equals space 9
    i.e.,        straight x squared plus straight y squared space equals 9 over 4                                                          ...(2)
    From (1) and (2), we get,
                                    straight x squared plus 4 straight x equals 9 over 4 space or space 4 straight x squared plus 16 straight x minus 9 space equals space 0
    therefore space space space space straight x space equals fraction numerator negative 16 plus-or-minus square root of 256 plus 144 end root over denominator 8 end fraction equals fraction numerator negative 16 plus-or-minus 20 over denominator 8 end fraction equals 1 half comma space minus 9 over 2
    therefore space space from space left parenthesis 1 right parenthesis comma space space space space space straight y squared space equals 1 half space space space space space space space space space space space space space space space space space open square brackets because straight y squared equals negative 9 over 2 space does space not space give space real space points close square brackets
because space straight y space equals space fraction numerator 1 over denominator square root of 2 end fraction comma space minus fraction numerator 1 over denominator square root of 2 end fraction
    therefore  curve (1) and (2) intersect in the points
                      straight P open parentheses 1 half comma space fraction numerator 1 over denominator square root of 2 end fraction close parentheses space space space and space space space straight Q open parentheses 1 half comma space minus fraction numerator 1 over denominator square root of 2 end fraction close parentheses
    From P, draw PM space perpendicular space straight x minus axis
    Here OA = 3 over 2

    Required area = Area of shaded region
                           = 2 (area of region OAPO)
                           = 2 [area of region OMPO + area of region MAPM]
                            equals space 2 open square brackets integral subscript 0 superscript 1 divided by 2 end superscript 2 square root of straight x space dx plus integral subscript 1 divided by 2 end subscript superscript 3 divided by 2 end superscript square root of 9 over 4 minus straight x squared end root close square brackets space equals space 4 integral subscript 0 superscript 1 divided by 2 end superscript straight x to the power of 1 divided by 2 end exponent plus 2 space integral subscript 1 divided by 2 end subscript superscript 3 divided by 2 end superscript square root of open parentheses 3 over 2 close parentheses squared minus straight x squared end root dx
                            equals 4 open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript 1 half end superscript plus 2 open square brackets fraction numerator straight x square root of begin display style 9 over 4 end style minus straight x squared end root over denominator 2 end fraction plus open parentheses begin display style 3 over 2 end style close parentheses squared over 2 sin to the power of negative 1 end exponent open parentheses fraction numerator straight x over denominator 3 divided by 2 end fraction close parentheses close square brackets subscript 1 half end subscript superscript 3 over 2 end superscript
    equals space 8 over 3 open square brackets straight x to the power of 3 divided by 2 end exponent close square brackets subscript 0 superscript 1 divided by 2 end superscript plus 2 open square brackets 1 half straight x square root of 9 over 4 minus straight x squared end root plus 9 over 8 sin to the power of negative 1 end exponent open parentheses fraction numerator 2 straight x over denominator 3 end fraction close parentheses close square brackets subscript 1 half end subscript superscript 3 over 2 end superscript
equals space 8 over 3 open square brackets open parentheses 1 half close parentheses to the power of 3 over 2 end exponent minus 0 close square brackets space plus 2 open square brackets open parentheses 0 plus 9 over 8 sin to the power of negative 1 end exponent 1 close parentheses minus open curly brackets 1 fourth square root of 9 over 4 minus 1 fourth end root plus 9 over 8 sin to the power of negative 1 end exponent 1 third close curly brackets close square brackets
equals space 8 over 3 fraction numerator 1 over denominator 2 square root of 2 end fraction plus 2 open square brackets 9 over 8 cross times straight pi over 2 minus fraction numerator 1 over denominator 2 square root of 2 end fraction minus 9 over 8 sin to the power of negative 1 end exponent open parentheses 1 third close parentheses close square brackets
equals space fraction numerator 4 over denominator 3 square root of 2 end fraction plus fraction numerator 9 straight pi over denominator 8 end fraction minus fraction numerator 1 over denominator square root of 2 end fraction minus 9 over 4 sin to the power of negative 1 end exponent open parentheses 1 third close parentheses
equals space open parentheses fraction numerator 4 square root of 2 over denominator 6 end fraction minus fraction numerator square root of 2 over denominator 2 end fraction close parentheses plus fraction numerator 9 straight pi over denominator 8 end fraction minus 9 over 4 space sin to the power of negative 1 end exponent open parentheses 1 third close parentheses space equals fraction numerator square root of 2 over denominator 6 end fraction plus fraction numerator 9 straight pi over denominator 8 end fraction minus 9 over 4 sin to the power of negative 1 end exponent open parentheses 1 third close parentheses

    Question 66
    CBSEENMA12032787

    Find the area lying above x-axis and included between the circle x2 + y2 = 8 x and inside of the parabola y2 = 4 x.

    Solution

    The equation of circle is
    x2 + y2 = 8 x    ...(1)

    The equation of parabola is
    y2 = 4 x    ...(2)
    (1) can be written as
    (x2 - 8 x) + y2 = 0 or (x2 - 8 x + 16) + y2 = 16
    or (x - 4)2 + y2 = (4)2    ...(3)
    which is a circle with centre C(4, 0) and radius = 4.
    From (1) and (2), we get,
    x2 + 4 x = 8 x or x2 - 4 x = 0 ⇒ x(x - 4) = 0
    ∴ x = 0, 4
    ∴ from (2), y =0, 4
    ∴ points of intersection of circle (1) and parabola (2) and 0(0, 0) and P(4, 4), above the x-axis.
    Required area =  area of region OPQCO
                          = (area of region OCPO) + (area of region PCQP)
                           equals space integral subscript 0 superscript 4 straight y space dx plus integral subscript 4 superscript 8 straight y space dx
equals space 2 integral subscript 0 superscript 4 square root of straight x space dx space plus space integral subscript 4 superscript 8 square root of left parenthesis 4 right parenthesis squared minus left parenthesis straight x minus 4 right parenthesis squared end root space dx space space space space space space space space space space space left square bracket because space of space left parenthesis 2 right parenthesis comma space left parenthesis 3 right parenthesis right square bracket
equals space 2 open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript 4 space plus space open square brackets fraction numerator left parenthesis straight x minus 4 right parenthesis over denominator 2 end fraction square root of left parenthesis 4 right parenthesis squared minus left parenthesis straight x minus 4 right parenthesis squared end root plus fraction numerator left parenthesis 4 right parenthesis squared over denominator 2 end fraction. sin to the power of negative 1 end exponent fraction numerator straight x minus 4 over denominator 4 end fraction close square brackets subscript 4 superscript 8
space equals space 4 over 3 open square brackets straight x to the power of 3 over 2 end exponent close square brackets subscript 0 superscript 4 plus open square brackets open parentheses fraction numerator 8 minus 4 over denominator 2 end fraction close parentheses square root of 16 minus 16 end root plus 8 space sin to the power of negative 1 end exponent left parenthesis 1 right parenthesis close square brackets space minus space open square brackets 0 plus 8 space sin to the power of negative 1 end exponent 0 close square brackets
equals space 4 over 3 open square brackets left parenthesis 4 right parenthesis to the power of 3 over 2 end exponent minus 0 close square brackets plus open parentheses 0 plus 8 cross times straight pi over 2 close parentheses minus left parenthesis 0 plus 0 right parenthesis
equals space 4 over 3 cross times 8 plus 4 straight pi equals space 32 over 3 plus 4 straight pi space equals space 4 over 3 left parenthesis 8 plus 3 straight pi right parenthesis space sq. space units. space

     
    Question 67
    CBSEENMA12032790

    Calculate the area enclosed in the region:
    open curly brackets left parenthesis straight x comma space straight y right parenthesis space semicolon space space straight x squared plus straight y squared space less or equal than space 1 space less than space straight x plus 1 half straight y close curly brackets

    Solution

    We are able to find the area included between the curves
                                   straight x squared plus straight y squared space equals space 1                                 ...(1)
    and                          straight x plus 1 half straight y space equals space 1                               ...(2)
    From (1) and (2), we get,
                        open parentheses 1 minus 1 half straight y close parentheses squared space plus space straight y squared space equals space 1 space space space space space therefore space space space space 1 space plus straight y squared over 4 minus straight y plus straight y squared space equals space 1
    therefore space space space 5 straight y squared minus 4 straight y space equals space 0 space space space space space rightwards double arrow space space space space space straight y left parenthesis 5 straight y minus 4 right parenthesis space equals space 0 space space rightwards double arrow space space space straight y space equals space 0 comma space 4 over 5
therefore space space from space left parenthesis 2 right parenthesis comma space space straight x space equals space 1 comma space space space 3 over 5
    therefore circle (1) and line (2) intersect in points A (1, 0) and straight B open parentheses 3 over 5 comma space 4 over 5 close parentheses
    Required area is shaded.
    Required area = integral subscript 3 divided by 5 end subscript superscript 1 square root of 1 minus straight x squared end root space dx minus integral subscript 3 divided by 5 end subscript superscript 1 2 space left parenthesis 1 minus straight x right parenthesis space dx                     equals space open square brackets fraction numerator straight x square root of 1 minus straight x squared end root over denominator 2 end fraction plus 1 half sin to the power of negative 1 end exponent straight x close square brackets subscript 3 over 5 end subscript superscript 1 space plus space open square brackets left parenthesis 1 minus straight x squared right parenthesis close square brackets subscript 3 divided by 5 end subscript superscript 1
equals space open parentheses 0 plus 1 half sin to the power of negative 1 end exponent 1 close parentheses space minus space open parentheses 1 half 3 over 5 square root of 1 minus 9 over 25 end root plus 1 half sin to the power of negative 1 end exponent 3 over 5 close parentheses plus open parentheses 0 minus 4 over 25 close parentheses
equals space 1 half. straight pi over 2 minus 3 over 10.4 over 5 minus straight i over 2 sin to the power of negative 1 end exponent 3 over 5 minus 4 over 25 equals space open parentheses straight pi over 4 minus 2 over 5 minus 1 half sin to the power of negative 1 end exponent 3 over 5 close parentheses space sq. space units. space

    Question 68
    CBSEENMA12032791

    Find the area of the circle x2 + y2 = 16 which is exterior to the parabola y2 = 6x. 

    Solution

    The equation of circle is
              straight x squared plus straight y squared space equals 16                    ...(1)
    The equation of parabola is
                  straight y squared space equals 6 straight x                         ...(2)
    From (1) and (2),
                   straight x squared plus 6 straight x space equals space 16
    or        straight x squared plus 6 straight x minus 16 space equals space 0
    therefore space space space left parenthesis straight x plus 8 right parenthesis space left parenthesis straight x minus 2 right parenthesis space equals space 0
    rightwards double arrow                        straight x equals negative 8 comma space 2

    Rejecting x = -8 as parabola lies in 1st or 4th quadrant , we get x =2
    When          straight x equals 2 comma space space straight y equals square root of 12 space equals space 2 square root of 3
    therefore space space left parenthesis 1 right parenthesis space and space left parenthesis 2 right parenthesis space intersect space in space straight P left parenthesis 2 comma space 2 square root of 3 right parenthesis
    Required Area = Area of the circle - area of circle interior to the parabola   
    equals 16 straight pi minus 2 integral subscript 0 superscript 2 straight y space dx space minus space 2 integral subscript 2 superscript 4 straight y space dx space equals space 16 straight pi minus 2 integral subscript 0 superscript 2 square root of 6 straight x to the power of 1 half end exponent dx minus 2 integral subscript 0 superscript 4 square root of 16 minus straight x squared end root dx
    equals 16 straight pi minus 2 square root of 6 open square brackets 2 over 3 straight x to the power of 3 over 2 end exponent close square brackets subscript 0 superscript 2 minus space 2 open square brackets straight x over 2 square root of 16 minus straight x squared end root plus 16 over 2 sin to the power of negative 1 end exponent straight x over 4 close square brackets subscript 2 superscript 4
equals space 16 straight pi minus 4 over 3 square root of 6. space 2 square root of 2 minus 2 open square brackets 4 over 2 square root of 16 minus 16 end root plus 16 over 2 sin to the power of negative 1 end exponent 1 minus 2 over 2 square root of 16 minus 4 end root minus 16 over 2 sin to the power of negative 1 end exponent 2 over 4 close square brackets
equals 16 straight pi minus fraction numerator 16 over denominator square root of 3 end fraction minus 16. space straight pi over 2 plus 4 square root of 3 plus fraction numerator 8 straight pi over denominator 3 end fraction equals negative fraction numerator 4 over denominator square root of 3 end fraction plus fraction numerator 32 space straight pi over denominator 3 end fraction space equals 4 over 3 left parenthesis 8 straight pi minus square root of 3 right parenthesis

    Question 69
    CBSEENMA12032795

    Find the area of the circle 4x2 + 4y2 = 9 which is interior to the parabola y2= 4 x. 

    Solution

    Consider the equations
               straight y squared space equals space 4 straight x                                   ...(1)
    and    4 straight x squared plus 4 straight y squared equals 9
    i.e.,    straight x squared plus straight y squared space equals space 9 over 4                           ...(2)
    From (1) and (2), we get,
                  straight x squared plus 4 straight x equals 9 over 4 space or space space 4 straight x squared plus 16 straight x minus 9 space equals space 0
    therefore space space space straight x space equals space fraction numerator negative 16 plus-or-minus square root of 256 plus 144 end root over denominator 8 end fraction equals fraction numerator negative 16 plus-or-minus 20 over denominator 8 end fraction equals space 1 half comma space minus 9 over 2
    therefore space space space space from space left parenthesis 1 right parenthesis comma space space space straight y squared space equals space 1 half                     open square brackets because space space straight y squared equals negative 9 over 2 space does space not space give space real space points close square brackets

    therefore space space space space straight y space equals space fraction numerator 1 over denominator square root of 2 end fraction comma space minus fraction numerator 1 over denominator square root of 2 end fraction
    therefore space space space space curve space left parenthesis 1 right parenthesis space and space left parenthesis 2 right parenthesis space intersect space in space the space points
                       straight P open parentheses 1 half comma space fraction numerator 1 over denominator square root of 2 end fraction close parentheses space and space straight Q space equals space open parentheses 1 half comma space minus fraction numerator 1 over denominator square root of 2 end fraction close parentheses
    From P, draw PM space perpendicular space straight x minus axis
    Here OA space equals space 3 over 2
    Required area = Area of shaded region
    = 2 (area of region OAPO) = 2 [area of region OMPO + area of region MAPM]
    equals space 2 open square brackets integral subscript 0 superscript 1 divided by 2 end superscript 2 square root of straight x dx plus integral subscript 1 divided by 2 end subscript superscript 3 divided by 2 end superscript square root of 9 over 4 minus straight x squared end root close square brackets space equals space 4 integral subscript 0 superscript 1 divided by 2 end superscript straight x to the power of 1 divided by 2 end exponent dx plus 2 integral subscript 1 divided by 2 end subscript superscript 3 divided by 2 end superscript square root of open parentheses 3 over 2 close parentheses squared minus straight x squared end root dx
equals space 4 open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript 1 half end superscript plus 2 open square brackets fraction numerator straight x square root of begin display style 9 over 4 minus straight x squared end style end root over denominator 2 end fraction plus open parentheses begin display style 3 over 2 end style close parentheses squared over 2 sin to the power of negative 1 end exponent open parentheses fraction numerator straight x over denominator 3 divided by 2 end fraction close parentheses close square brackets subscript 1 half end subscript superscript 3 over 2 end superscript
equals space 8 open square brackets straight x to the power of 3 divided by 2 end exponent close square brackets subscript 0 superscript 1 divided by 2 end superscript space plus space 2 space open square brackets 1 half straight x square root of 9 over 4 minus straight x squared end root plus 9 over 8 sin to the power of negative 1 end exponent open parentheses fraction numerator 2 straight x over denominator 3 end fraction close parentheses close square brackets subscript 1 half end subscript superscript 3 over 2 end superscript
equals space 8 over 3 open square brackets open parentheses 1 half close parentheses to the power of 3 over 2 end exponent minus 0 close square brackets plus space 2 open square brackets open parentheses 0 plus 9 over 8 sin to the power of negative 1 end exponent 1 close parentheses minus open curly brackets 1 fourth square root of 9 over 4 minus 1 fourth end root plus 9 over 8 sin to the power of negative 1 end exponent 1 third close curly brackets close square brackets
equals space 8 over 3 fraction numerator 1 over denominator 2 square root of 2 end fraction plus 2 open square brackets 9 over 8 cross times straight pi over 2 minus fraction numerator 1 over denominator 2 square root of 2 end fraction minus 9 over 8 sin to the power of negative 1 end exponent open parentheses 1 third close parentheses close square brackets
equals space fraction numerator 4 over denominator 3 square root of 2 end fraction plus fraction numerator 9 straight pi over denominator 8 end fraction minus fraction numerator 1 over denominator square root of 2 end fraction minus 9 over 4 sin to the power of negative 1 end exponent open parentheses 1 third close parentheses
equals space open parentheses fraction numerator 4 square root of 2 over denominator 6 end fraction minus fraction numerator square root of 2 over denominator 2 end fraction close parentheses plus fraction numerator 9 straight pi over denominator 8 end fraction minus 9 over 4 sin to the power of negative 1 end exponent open parentheses 1 third close parentheses space equals space fraction numerator square root of 2 over denominator 6 end fraction plus fraction numerator 9 straight pi over denominator 8 end fraction minus 9 over 4 sin to the power of negative 1 end exponent open parentheses 1 third close parentheses

    Question 70
    CBSEENMA12032798

    Draw a rough sketch of the region {(x, y): y2 ≤ 5 x, 5 x2 + 5 y2 ≤ 36} and find the area enclosed by the region using method of integration.

    Solution

    Given region is
                    open curly brackets left parenthesis straight x comma space straight y right parenthesis space colon space straight y squared less or equal than 5 straight x comma space 5 straight x squared plus 5 straight y squared space less or equal than 36 close curly brackets
    Consider the equations
                       straight y squared space equals space 5 straight x                        ...(1)
                     5 straight x squared plus 5 straight y squared space equals space 36
       i.e.           straight x squared plus straight y squared space equals space 36 over 5               ...(2)
    From (1) and (2), we get,
                            5 straight x squared plus 25 straight x space equals space 36 space space space or space space 5 straight x squared plus 25 straight x minus 36 space equals space 0
    therefore space space space straight x space equals space fraction numerator negative 25 plus-or-minus square root of 625 plus 720 end root over denominator 10 end fraction equals space fraction numerator negative 25 plus-or-minus square root of 1345 over denominator 10 end fraction
    Rejecting negative value of x, we get,
    straight x equals fraction numerator negative 25 plus square root of 1345 over denominator 10 end fraction equals straight a space left parenthesis say right parenthesis

    which gives the abscissa of the points of intersection P and Q.
    Required area = Area of shaded region = 2 (area of region OAPO)
    = 2[area of region OMPO + area of region MAPM]
                           equals space 2 open square brackets integral subscript 0 superscript straight a square root of 5 square root of straight x dx plus integral subscript straight a superscript 6 divided by square root of 5 end superscript square root of 36 over 5 minus straight x squared end root close square brackets dx
                         equals space 2 square root of 5 open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript straight a plus 2 open square brackets fraction numerator straight x square root of begin display style 36 over 5 end style minus straight x squared end root over denominator 2 end fraction plus fraction numerator begin display style 36 over 5 end style over denominator 2 end fraction sin to the power of negative 1 end exponent open parentheses fraction numerator straight x over denominator 6 divided by square root of 5 end fraction close parentheses close square brackets subscript straight a superscript fraction numerator 6 over denominator square root of 5 end fraction end superscript
equals space fraction numerator 4 square root of 5 over denominator 3 end fraction left parenthesis straight a to the power of 3 over 2 end exponent minus 0 right parenthesis space space plus open square brackets open parentheses 0 plus 36 over 5 sin to the power of negative 1 end exponent 1 close parentheses space minus space straight a square root of 36 over 5 minus straight a squared end root sin to the power of negative 1 end exponent open parentheses fraction numerator straight a square root of 5 over denominator 6 end fraction close parentheses close square brackets
equals space fraction numerator 4 square root of 5 over denominator 3 end fraction straight a to the power of 3 divided by 2 end exponent plus 36 over 10 straight pi minus straight a square root of 36 over 5 minus straight a squared end root minus 36 over 5 sin to the power of negative 1 end exponent open parentheses fraction numerator straight a square root of 5 over denominator 6 end fraction close parentheses
    where straight a equals fraction numerator negative 25 plus square root of 1345 over denominator 10 end fraction

    Question 71
    CBSEENMA12032799

    Draw a rough sketch of the region {(x, y): y2 ≤ 3 x, 3 x2 + 3 y2 ≤ 16} and find the area enclosed by the region using method of integration.

    Solution

    Given region is
                     open curly brackets left parenthesis straight x comma space straight y right parenthesis space colon space straight y squared less or equal than 3 straight x comma space 3 straight x squared plus 3 straight y squared less or equal than 16 close curly brackets
    Consider the equations
                            straight y squared equals 3 space straight x comma space                   ...(1)
                  3 straight x squared plus 3 straight y squared space equals space 16
    i.e.,     straight x squared plus straight y squared space equals space 16 over 3                      ...(2)
    From (1) and (2), we get,
                         straight x squared plus 3 straight x space equals space 16 over 3 space space space or space space 3 straight x squared plus 9 straight x minus 16 space equals space 0
    therefore space space straight x space equals space fraction numerator negative 9 plus-or-minus square root of 81 plus 192 end root over denominator 6 end fraction space equals fraction numerator negative 9 plus-or-minus square root of 273 over denominator 6 end fraction
    Rejecting negative values of x, we get
    straight x equals fraction numerator negative 9 plus square root of 273 over denominator 6 end fraction equals space straight a

    which gives the abscissa of the points of intersection P and Q.
    Required area  = Area of shaded region
    = 2 [area of region APOA]
    = 2 [area of region AMPA + area of region MOPM ]
     = 2 open square brackets integral subscript 0 superscript straight a square root of 3 space square root of straight x dx plus space integral subscript straight a superscript 4 divided by square root of 3 end superscript square root of 16 over 3 minus straight x squared end root space dx close square brackets
    =  2 square root of 3 open square brackets fraction numerator straight x to the power of 3 divided by 2 end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript straight a plus 2 open square brackets fraction numerator straight x square root of begin display style 16 over 3 end style minus straight x squared end root over denominator 2 end fraction plus fraction numerator begin display style 16 over 3 end style over denominator 2 end fraction sin to the power of negative 1 end exponent open parentheses fraction numerator straight x over denominator 4 divided by square root of 3 end fraction close parentheses close square brackets subscript 0 superscript fraction numerator 4 over denominator square root of 3 end fraction end superscript
    equals space fraction numerator 4 over denominator square root of 3 end fraction left parenthesis straight a to the power of 3 divided by 2 end exponent minus 0 right parenthesis space plus space open square brackets open curly brackets 0 plus 16 over 3 sin to the power of negative 1 end exponent left parenthesis 1 right parenthesis close curly brackets minus open curly brackets straight a square root of 16 over 3 minus straight a squared end root plus 16 over 3 sin to the power of negative 1 end exponent open parentheses fraction numerator straight a square root of 3 over denominator 4 end fraction close parentheses close curly brackets close square brackets
equals space fraction numerator 4 over denominator square root of 3 end fraction straight a to the power of 3 divided by 2 end exponent plus 8 over 3 straight pi minus straight a square root of 16 over 3 minus straight a squared end root minus 16 over 3 sin to the power of negative 1 end exponent open parentheses fraction numerator straight a square root of 3 over denominator 4 end fraction close parentheses

    Question 72
    CBSEENMA12032801

    Find the area of the smaller part of the circle x2 + y2 = a cut oil by the line straight x equals fraction numerator straight a over denominator square root of 2 end fraction

    Solution

    The equation of circle is
                       straight x squared minus straight y squared space equals straight a squared                 ...(1)
      The equation of line is
                          straight x space equals space fraction numerator straight a over denominator square root of 2 end fraction                   ...(2)
    From (1) and (2), we get,
                         straight a squared over 2 minus straight y squared space equals space straight a squared space space space space or space space space straight y squared space equals space straight a squared over 2
    therefore space space space space space straight y space equals space fraction numerator straight a over denominator square root of 2 end fraction
    because space space space straight C is open parentheses fraction numerator straight a over denominator square root of 2 end fraction comma space fraction numerator straight a over denominator square root of 2 end fraction close parentheses

     equals space 2 integral subscript fraction numerator straight a over denominator square root of 2 end fraction end subscript superscript straight a straight y space dx space equals space 2 integral subscript fraction numerator straight a over denominator square root of 2 end fraction end subscript superscript straight a square root of straight a squared minus straight x squared end root dx
    equals space 2 open square brackets fraction numerator straight x square root of straight a squared minus straight x squared end root over denominator 2 end fraction plus straight a squared over 2 sin to the power of negative 1 end exponent straight x over straight a close square brackets subscript fraction numerator straight a over denominator square root of 2 end fraction end subscript superscript straight a
equals space 2 open parentheses fraction numerator straight a square root of straight a squared minus straight a squared end root over denominator 2 end fraction plus straight a squared over 2 sin to the power of negative 1 end exponent 1 close parentheses space minus space 2 open parentheses fraction numerator straight a over denominator 2 square root of 2 end fraction square root of straight a squared minus straight a squared over 2 end root plus straight a squared over 2 sin to the power of negative 1 end exponent fraction numerator 1 over denominator square root of 2 end fraction close parentheses
equals space 2 open parentheses 0 plus straight a squared over 2 cross times straight pi over 2 close parentheses minus 2 open parentheses fraction numerator straight a over denominator 2 square root of 2 end fraction cross times fraction numerator straight a over denominator square root of 2 end fraction plus straight a squared over 2 cross times straight pi over 4 close parentheses
equals space πa squared over 2 minus straight a squared over 2 minus πa squared over 4 space equals space πa squared over 4 minus straight a squared over 2
    equals space straight a squared over 4 left parenthesis straight pi minus 2 right parenthesis space sq. space units
                         

    Question 73
    CBSEENMA12032803

    Find the area of the smaller region bounded by the ellipse straight x squared over 9 plus straight y squared over 4 space equals space 1 and the straight line straight x over 3 plus straight y over 2 space equals space 1.

    Solution

    The equation of ellipse is
                    straight x squared over 9 plus straight y squared over 4 space equals space 1                   ...(1)
     The equation of line is
                  straight x over 3 plus straight y over 2 space equals space 1                       ...(2)
    Let line (2) meet ellipse (1) in A (3, 0) and B(0, 2).
             Area of shaded region = Area of region OAB - area of increment OAB

    equals space 2 over 3 integral subscript 0 superscript 3 square root of 9 minus straight x squared end root space dx minus space 2 over 3 integral subscript 0 superscript 3 left parenthesis 3 minus straight x right parenthesis space dx                       open square brackets because space of space left parenthesis 1 right parenthesis comma space left parenthesis 2 right parenthesis close square brackets
    equals space 2 over 3 open square brackets fraction numerator straight x square root of 9 minus straight x squared end root over denominator 2 end fraction plus 9 over 2 sin to the power of negative 1 end exponent straight x over 3 close square brackets subscript 0 superscript 3 space minus space 2 over 3 open square brackets fraction numerator left parenthesis 2 minus straight x right parenthesis squared over denominator left parenthesis negative 1 right parenthesis thin space left parenthesis 2 right parenthesis end fraction close square brackets subscript 0 superscript 3
equals space 2 over 3 open square brackets open parentheses fraction numerator 3 square root of 9 minus 9 end root over denominator 2 end fraction plus 9 over 2 sin to the power of negative 1 end exponent 1 close parentheses minus open parentheses 0 plus 9 over 2 sin to the power of negative 1 end exponent 0 close parentheses close square brackets plus 1 third left square bracket 0 minus 9 right square bracket
space equals space 2 over 3 open square brackets open parentheses 0 plus 9 over 2 cross times straight pi over 2 close parentheses minus left parenthesis 0 plus 0 right parenthesis close square brackets plus 1 third left parenthesis 0 minus 9 right parenthesis
equals space 2 over 3 cross times 9 over 2 cross times straight pi over 2 minus 1 third space equals space fraction numerator 3 straight pi over denominator 2 end fraction minus 3
equals space fraction numerator 3 space straight pi minus 6 over denominator 2 end fraction space equals 3 over 2 left parenthesis straight pi minus 2 right parenthesis space sq. space units.

    Question 74
    CBSEENMA12032804

    Using integration, find the area of the smaller region bounded by the curve straight x squared over 16 plus straight y squared over 9 space equals space 1 and the straight line straight x over 4 plus straight y over 3 equals 1.

    Solution

    The equation of ellipse is
                    straight x squared over 16 plus straight y squared over 9 equals 1                          ...(1)
    The equation of line is
                   straight x over 4 plus straight y over 3 equals 1                               ...(2)

    Let line (2) meet ellipse (1) in
    A(4, 0) and B(0, 3)
    Area of shaded region = Area of region OAB - area of increment space OAB
           equals space 3 over 4. integral subscript 0 superscript 4 square root of 16 minus straight x squared end root space dx space minus space 3 over 4 integral subscript 0 superscript 4 left parenthesis 4 minus straight x right parenthesis space dx    open square brackets because space space of space left parenthesis 1 right parenthesis comma space left parenthesis 2 right parenthesis close square brackets
             equals space 3 over 4 open square brackets fraction numerator straight x square root of 16 minus straight x squared end root over denominator 2 end fraction plus 16 over 2 sin to the power of negative 1 end exponent straight x over 4 close square brackets subscript 0 superscript 4 minus space 3 over 4 open square brackets fraction numerator left parenthesis 4 minus straight x right parenthesis squared over denominator left parenthesis negative 1 right parenthesis thin space left parenthesis 2 right parenthesis end fraction close square brackets subscript 0 superscript 4
equals space 3 over 4 open square brackets open parentheses 0 plus 8 cross times straight pi over 2 close parentheses minus left parenthesis 0 plus 0 right parenthesis close square brackets plus 6
equals space 3 straight pi space plus 6 space equals space 3 space left parenthesis straight pi plus 2 right parenthesis space square space units.

    Question 75
    CBSEENMA12032806

    Find the area of smaller region bounded by the ellipse straight x squared over straight a squared plus straight y squared over straight b squared space equals 1 and the straight line straight x over straight a plus straight y over straight b equals 1

    Solution

    Consider the equations
                     straight x squared over straight a squared plus straight y squared over straight b squared space equals space 1                             ...(1)
    and       straight x over straight a plus straight y over straight b equals 1                                       ...(2)

    Line (2) meets ellipse (1) in A (a, 0) and B (0, b)
    Area of shaded region = Area of region OAB area of ∆OAB
                                    equals space straight b over straight a integral subscript 0 superscript straight a square root of straight a squared minus straight x squared end root space dx minus straight b over straight a integral subscript 0 superscript straight a left parenthesis straight a minus straight x right parenthesis space dx
equals space straight b over straight a open square brackets fraction numerator straight x square root of straight a squared minus straight x squared end root over denominator 2 end fraction plus straight a squared over 2 sin to the power of negative 1 end exponent straight x over straight a close square brackets subscript 0 superscript straight a minus space fraction numerator straight b over denominator 2 straight a end fraction open square brackets fraction numerator left parenthesis straight a minus straight x right parenthesis squared over denominator 1 end fraction close square brackets subscript 0 superscript straight a
equals space straight b over straight a open square brackets open parentheses 0 plus straight a squared over 2 sin to the power of negative 1 end exponent 1 close parentheses minus open parentheses 0 plus straight a squared over 2 sin to the power of negative 1 end exponent 0 close parentheses close square brackets plus fraction numerator straight b over denominator 2 straight a end fraction left square bracket 0 minus straight a squared right square bracket
equals space straight b over straight a open square brackets straight a squared over 2 cross times straight pi over 2 minus 0 minus 0 close square brackets space minus space ab over 2 space equals space πab over 4 minus ab over 2 space equals space ab over 4 left parenthesis straight pi minus 2 right parenthesis space sq. space units.
    which is required area. 

    Question 76
    CBSEENMA12032807

    Evaluate integral subscript 0 superscript straight r square root of straight r squared minus straight x squared end root dx,  where x is a fixed positive number, Hence, prove that the area of a circle of radius r is straight pi space straight r squared.

    Solution

    Let I = integral subscript 0 superscript straight r square root of straight r squared minus straight x squared end root space dx
              equals space open square brackets fraction numerator straight x square root of straight r squared minus straight x squared end root over denominator 2 end fraction plus straight r squared over 2. sin to the power of negative 1 end exponent open parentheses straight x over straight r close parentheses close square brackets subscript 0 superscript straight r
equals space open square brackets fraction numerator straight r square root of straight r squared minus straight r squared end root over denominator 2 end fraction plus straight r squared over 2 sin to the power of negative 1 end exponent open parentheses straight r over straight r close parentheses close square brackets space minus space open square brackets 0 plus straight r squared over 2 sin to the power of negative 1 end exponent left parenthesis 0 right parenthesis close square brackets
space equals space open square brackets 0 plus straight r squared over 2 sin to the power of negative 1 end exponent left parenthesis 1 right parenthesis close square brackets space minus space open square brackets 0 plus straight r squared over 2 sin to the power of negative 1 end exponent left parenthesis 0 right parenthesis close square brackets space equals space 0 plus straight r squared over 2 cross times straight pi over 2 minus 0 space equals space πr squared over 4

    Let straight f left parenthesis straight x right parenthesis space equals space straight y space equals space square root of straight r squared minus straight x squared end root
    Now straight y equals space square root of straight r squared minus straight x squared end root   rightwards double arrow space space space straight y squared space equals space straight r squared minus straight x squared
    rightwards double arrow space space space space space straight x squared plus straight y squared space equals space straight r squared comma space space which space is space straight a space circle space at space the space origin space and space radius space straight r.
    therefore space space space space integral subscript 0 superscript straight r square root of straight r squared minus straight x squared end root space space dx  represents the area bounded  by the circle straight x squared plus straight y squared space equals space straight r squared comma the x-axis and the ordinate x = 0 and the ordinate x = r, i.e., it represents the area of the region in the first quadrant. 
    therefore space space space space area space of space circle space equals space 4. space open parentheses πr squared over 4 close parentheses space equals space straight pi space straight r squared.

    Question 77
    CBSEENMA12032808

    Find the whole area of the circle x2 + y2 = a2.

    Solution
    The equation of circle is x2 + y2 = a2     ...(1)
    Its centre is origin and radius a. We know that circle x2 + y2 = a2 is symmetrical about both axes.
    therefore space space space required space area space equals space 4 space integral subscript 0 superscript straight a straight y space dx space equals space 4 space integral subscript 0 superscript straight a square root of straight a squared minus straight x squared end root space dx
                      equals space 4 open square brackets fraction numerator straight x square root of straight a squared minus straight x squared end root over denominator 2 end fraction plus straight a squared over 2 sin to the power of negative 1 end exponent straight x over straight a close square brackets subscript 0 superscript straight a
equals space 4 open square brackets open parentheses 0 plus straight a squared over 2 sin to the power of negative 1 end exponent 1 close parentheses space minus space open parentheses 0 plus straight a squared over 2 sin to the power of negative 1 end exponent 0 close parentheses close square brackets
equals space 4 open square brackets open parentheses 0 plus straight a squared over 2 sin to the power of negative 1 end exponent 1 close parentheses space minus space open parentheses 0 plus straight a squared over 2 sin to the power of negative 1 end exponent 0 close parentheses close square brackets
equals 4 space open square brackets straight a squared over 2 cross times straight pi over 2 close square brackets space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space sin to the power of negative 1 end exponent 0 space equals space 0 close square brackets
space equals space straight pi space straight a space.


    Question 78
    CBSEENMA12032809

    Area lying in the first quadrant and bounded by the circle x2 + y2 = 4 and the lines x = 0 and x = 2 is
    • straight pi
    • straight pi over 2
    • straight pi over 3
    • straight pi over 4

    Solution

    A.

    straight pi

    The equation of circle is
                      straight x squared plus straight y squared space equals space 4                   ...(1)
    We are to find the area of the circle lying between the lines x = 0 and x = 2 in the first quadrant. 
    Required area = integral subscript 0 superscript 2 straight y space dx
                           equals space integral subscript 0 superscript 2 square root of 4 minus straight x squared space end root dx                               open square brackets because space space space of space left parenthesis 1 right parenthesis close square brackets

                            equals space integral subscript 0 superscript 2 square root of left parenthesis 2 right parenthesis squared minus straight x squared end root space dx space equals space open square brackets straight x over 2 square root of left parenthesis 2 right parenthesis squared minus straight x squared end root plus fraction numerator left parenthesis 2 right parenthesis squared over denominator 2 end fraction sin to the power of negative 1 end exponent open parentheses straight x over 2 close parentheses close square brackets subscript 0 superscript 2
space equals open square brackets straight x over 2 square root of 4 minus straight x squared end root plus 2 space sin to the power of negative 1 end exponent open parentheses straight x over 2 close parentheses close square brackets subscript 0 superscript 2
equals space open square brackets 2 over 2 square root of 4 minus 4 end root plus 2 space sin to the power of negative 1 end exponent open parentheses 2 over 2 close parentheses close square brackets space minus space open square brackets 0 plus 2 space sin to the power of negative 1 end exponent 0 close square brackets
equals space open square brackets 0 plus 2 space sin to the power of negative 1 end exponent left parenthesis 1 right parenthesis space minus space left square bracket 0 plus 2 space cross times 0 right square bracket close square brackets
equals space 2 space sin to the power of negative 1 end exponent 1 space equals space 2 space cross times straight pi over 2 space equals space straight pi

    Question 79
    CBSEENMA12032810

    Area of the region bounded by the curve y2 = 4 x, y-axis and the line y = 3 is
    • 2

    • 9 over 4
    • 9 over 3
    • 9 over 4

    Solution

    B.

    9 over 4

    The equation of curve is
    y2 = 4.x
      We are to find the area bounded by the curve straight y squared space equals space 4 straight x comma space space straight y minus axis space and space the space line space straight y space equals space 3.
                           Required area  = integral subscript 0 superscript 3 straight x space dy space equals space integral subscript 0 superscript 3 straight y squared over 4 dy
                                                     equals space 1 fourth integral subscript 0 superscript 3 straight y squared space dy space space equals 1 fourth open square brackets straight y cubed over 3 close square brackets subscript 0 superscript 3
equals space 1 over 12 open square brackets straight y cubed close square brackets subscript 0 superscript 3 space equals space 1 over 12 left parenthesis 27 minus 0 right parenthesis
equals space 27 over 12 space equals 9 over 4
                   

    Sponsor Area

    Question 80
    CBSEENMA12032811

    Smaller area enclosed by the circle x2 + y2 = 4 and the line x + y = 2 is
    Choose the correct answer.
    or
    Draw the rough sketch and find the area of the region:
    {(x, y): x2 + y2 < 4, x + y > 2}.  

    • 2 space left parenthesis straight pi space minus space 2 right parenthesis
    • straight pi space minus 2
    • 2 straight pi minus 1
    • left parenthesis 2 straight pi plus 2 right parenthesis

    Solution

    B.

    straight pi space minus 2

    The equation of circle is
                                   straight x squared plus straight y squared space equals space 4                ...(1)
    Its centre is O(0, 0) and radius OA = OB = 2
    The equation of line is
                                    x + y = 2  ....(2)
    or    straight x over 2 plus straight y over 2 space equals 1
    therefore    line passes through A(2, 0),  B(0, 2).
    Required area  = area of circle in first quadrant - area increment OAB.
                              equals space integral subscript 0 superscript 2 square root of 4 minus straight x squared space space end root space dx space minus space integral subscript 0 superscript 2 left parenthesis 2 minus straight x right parenthesis space dx                  open square brackets because space of space left parenthesis 1 right parenthesis comma space left parenthesis 2 right parenthesis close square brackets
                              equals space integral subscript 0 superscript 2 square root of left parenthesis 2 right parenthesis squared minus straight x squared end root space dx space minus space integral subscript 0 superscript 2 left parenthesis 2 minus straight x right parenthesis space dx
                               equals space open square brackets straight x over 2 square root of left parenthesis 2 right parenthesis squared minus straight x squared end root plus fraction numerator left parenthesis 2 right parenthesis squared over denominator 2 end fraction sin to the power of negative 1 end exponent straight x over 2 close square brackets subscript 0 superscript 2 space minus space open square brackets 2 straight x minus straight x squared over 2 close square brackets subscript 0 superscript 2
equals space open square brackets 2 over 2 square root of 4 minus 4 end root plus 4 over 2 sin to the power of negative 1 end exponent 1 close square brackets space minus space open square brackets 0 plus 4 over 2 sin to the power of negative 1 end exponent 0 close square brackets space minus space open square brackets open parentheses 4 minus 4 over 2 close parentheses minus left parenthesis 0 minus 0 right parenthesis close square brackets
equals space open parentheses 0 plus 4 over 2 cross times straight pi over 2 close parentheses minus left parenthesis 0 plus 2 cross times 0 right parenthesis space minus space 2 plus 0 space equals space straight pi space minus space 2
                       

    Question 81
    CBSEENMA12032813

    Area lying between the curves y2 = 4x and y = 2x  is

    • 2 over 3
    • 1 third
    • 1 fourth
    • 3 over 4

    Solution

    B.

    1 third

    The equations of the curves are
                             straight y squared space equals space 4 straight x                         ...(1)
               and         straight y equals space 2 straight x                           ...(2)
    From (1) and (2),
                              4 straight x squared space equals space 4 straight x
    or               4 straight x left parenthesis straight x minus 1 right parenthesis space equals space 0.
    therefore space space space space space space space space space straight x space equals space 0 comma space space 1
therefore space space space from space left parenthesis 2 right parenthesis comma space space straight y space equals space 0 comma space 2
therefore space space space curves space left parenthesis 1 right parenthesis space and space left parenthesis 2 right parenthesis space intersect space in space straight O left parenthesis 0 comma space 0 right parenthesis comma space space space straight A left parenthesis 6 comma space 2 right parenthesis

    Required area  = integral subscript 0 superscript 1 straight y space dx space equals space integral subscript 0 superscript 1 2 space straight x space dx space equals space 2 space integral subscript 0 superscript 1 straight x to the power of 1 half end exponent dx minus 2 integral subscript 0 superscript 1 straight x space dx space equals space 2 open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript 1 space minus space 2 open square brackets straight x squared over 2 close square brackets subscript 0 superscript 1
                           equals space 4 over 3 open square brackets straight x to the power of 3 over 2 end exponent close square brackets subscript 0 superscript 1 space minus space open square brackets straight x squared close square brackets subscript 0 superscript 1 space equals space 4 over 3 left parenthesis 1 minus 0 right parenthesis minus space left parenthesis 1 minus 0 right parenthesis space equals space 4 over 3 minus 1 space equals space 1 third


    Question 82
    CBSEENMA12032815

    Area bounded by the curve y = x3  the x-axis and the ordinates x - 2 and a = 1 is
    • -9

    • fraction numerator negative 15 over denominator 4 end fraction
    • 15 over 4
    • 17 over 4

    Solution

    D.

    17 over 4

    We want to find the area bounded by the curve y = x3, the x-axis and the ordinates x = - 2 and x = 1.
    A rough sketch of the curve y = x3 is given in the figure.

    Required area  = integral subscript negative 2 end subscript superscript 1 space open vertical bar straight x cubed close vertical bar space dx space equals space integral subscript negative 2 end subscript superscript 0 open vertical bar straight x cubed close vertical bar space dx space plus space integral subscript 0 superscript 1 open vertical bar straight x close vertical bar cubed space dx space equals space integral subscript negative 2 end subscript superscript 0 left parenthesis negative straight x cubed right parenthesis space dx plus integral subscript 0 superscript 1 straight x cubed space dx
                             equals negative open square brackets straight x to the power of 4 over 4 close square brackets subscript 2 superscript 0 plus open square brackets straight x to the power of 4 over 4 close square brackets subscript 0 space equals space minus open square brackets 0 minus fraction numerator left parenthesis negative 2 right parenthesis to the power of 4 over denominator 4 end fraction close square brackets plus open square brackets 1 fourth minus 0 close square brackets space equals space 4 plus 1 fourth space equals space 17 over 4
    therefore space space space left parenthesis straight D right parenthesis space is space correct space answer.

    Question 83
    CBSEENMA12032817

    The area bounded by the curve y = x |x|, x-axis and the ordinates x = - 1 and x = 1 is given by
    • 0

    • 1 third
    • 2 over 3
    • 4 over 3

    Solution

    C.

    2 over 3

    We want to find the area bounded by the curve straight y equals straight x space open vertical bar straight x close vertical bar comma x-axis and the ordinates x = -1 and x = 1
    Required area = integral subscript negative 1 end subscript superscript 1 space straight y space dx space equals space integral subscript negative 1 end subscript superscript 1 space straight x space open vertical bar straight x close vertical bar space dx
                  equals space integral subscript negative 1 end subscript superscript 0 open vertical bar straight x open vertical bar straight x close vertical bar close vertical bar space dx space plus space integral subscript 0 superscript 1 space straight x space open vertical bar straight x close vertical bar space dx
                                          open square brackets because space space space open vertical bar straight x space open vertical bar straight x close vertical bar close vertical bar space equals space open vertical bar straight x close vertical bar space open vertical bar straight x close vertical bar space equals straight x squared close square brackets
                     equals space integral subscript negative 1 end subscript superscript 0 left parenthesis straight x squared right parenthesis dx plus integral subscript 0 superscript 1 straight x squared dx space equals space open square brackets straight x cubed over 3 close square brackets subscript negative 1 end subscript superscript 0 plus open square brackets straight x cubed over 3 close square brackets subscript 0 superscript 1
equals space open square brackets 0 minus fraction numerator left parenthesis negative 1 right parenthesis cubed over denominator 3 end fraction close square brackets plus open square brackets 1 third minus 0 close square brackets space equals space 1 third plus 1 third equals 2 over 3

    Question 84
    CBSEENMA12032819

    The area of the circle x +y =16 exterior to the parabola y2 = 6x is
    • 4 over 3 left parenthesis 4 straight pi minus square root of 3 right parenthesis
    • 4 over 3 left parenthesis 4 straight pi plus square root of 3 right parenthesis
    • 4 over 3 left parenthesis 8 straight pi minus square root of 3 right parenthesis
    • 4 over 3 left parenthesis 8 straight pi plus square root of 3 right parenthesis

    Solution

    C.

    4 over 3 left parenthesis 8 straight pi minus square root of 3 right parenthesis

    The equation of circle is
                         straight x squared plus straight y squared space equals space 16                     ...(1)
    The equation of parabola is
                      straight y squared space equals space 6 straight x                                  ...(2)
    From (1) and (2),
                    straight x squared plus 6 straight x space equals space 16
    or      straight x squared plus 6 straight x minus 16 space equals space 0
    therefore space space left parenthesis straight x plus 8 right parenthesis space left parenthesis straight x minus 2 right parenthesis space equals space 0
    rightwards double arrow                       x = -8, 2
    Rejecting x = -8 as parabola lies in 1st or 4th quadrant, we get x = 2
    When              x = 2,   straight y equals square root of 12 space equals space 2 square root of 3
    therefore   (1) and (2) intersect in straight P left parenthesis 2 comma space 2 square root of 3 right parenthesis
    Required Area = Area of the circle - area of circle interior to the parabola
                            equals space 16 straight pi minus 2 space integral subscript 0 superscript 2 straight y space dx space minus space 2 integral subscript 2 superscript 4 straight y space dx
equals space 16 straight pi minus 2 integral subscript 0 superscript 2 square root of 6 space straight x to the power of 1 half end exponent dx space minus space 2 integral subscript 0 superscript 4 square root of 16 minus straight x squared end root space dx
space equals space 16 straight pi space minus space 2 square root of 6 open square brackets 2 over 3 straight x to the power of 3 over 2 end exponent close square brackets subscript 0 superscript 2 space minus space 2 open square brackets straight x over 2 square root of 16 minus straight x squared end root plus 16 over 2 sin to the power of negative 1 end exponent straight x over 4 close square brackets subscript 2 superscript 4
    equals 16 straight pi minus 4 over 3 square root of 6. space 2 square root of 2 minus 2 open square brackets 4 over 2 square root of 16 minus 6 end root plus 16 over 2 sin to the power of negative 1 end exponent 1 minus 2 over 2 square root of 16 minus 4 end root minus 16 over 2 sin to the power of negative 1 end exponent 2 over 4 close square brackets
equals space 16 straight pi minus fraction numerator 16 over denominator square root of 3 end fraction minus 16. space straight pi over 2 plus 4 square root of 3 plus fraction numerator 8 straight pi over denominator 3 end fraction
equals negative fraction numerator 4 over denominator square root of 3 end fraction plus fraction numerator 32 straight pi over denominator 3 end fraction equals space 4 over 3 left parenthesis 8 straight pi minus square root of 3 right parenthesis

    Question 85
    CBSEENMA12032821

    The area bounded by the x-axis, y = cosx and y = sin x when 0 less or equal than straight x less or equal than straight pi over 2

    • 2 left parenthesis square root of 2 minus 1 right parenthesis
    • square root of 2 minus 1
    • square root of 2 plus 1
    • square root of 2

    Solution

    B.

    square root of 2 minus 1

    The two curves y = sin x and y = cos x meet where sin x = cos x ,  i.e.,  where x = 1
    rightwards double arrow space space space space straight x space equals space straight pi over 4.
    Required area (show shaded)
                                   equals space integral subscript 0 superscript straight pi over 4 end superscript left parenthesis cosx space minus space sinx right parenthesis space dx
equals space open square brackets sinx space plus space cosx close square brackets subscript 0 superscript straight pi over 4 end superscript space equals space sin space straight pi over 4 plus cos space straight pi over 4 minus left parenthesis 0 plus 1 right parenthesis
equals space fraction numerator 1 over denominator square root of 2 end fraction plus fraction numerator 1 over denominator square root of 2 end fraction minus 1 space equals space fraction numerator 2 over denominator square root of 2 end fraction minus 1 space equals space square root of 2 minus 1.

    Question 86
    CBSEENMA12032822

    Prove that the curves y2 = 4x and x2 = 4y divide the area of the square bounded by x = 0, x = 4, y = 4 and y = 0 into three equal parts.

    Solution

    The equation of curves are
                                  straight y squared space equals space 4 straight x                   ...(1)
                      and      straight x squared space equals space 4 straight y                  ...(2)
    From (2),  straight y equals straight x squared over 4                                 ...(3)
    Putting this value of y in (1),
    straight x to the power of 4 over 16 space equals space 4 straight x space space space or space space straight x to the power of 4 space equals space 64 straight x
    or   straight x left parenthesis straight x cubed minus 64 right parenthesis space equals space 0
    therefore space space space space straight x space equals space 0 comma space 4
therefore space space space from space left parenthesis 3 right parenthesis comma space space straight y space equals space 0 comma space space 4
because space space space curves space left parenthesis 1 right parenthesis space and space left parenthesis 2 right parenthesis space intersect space in space straight O left parenthesis 0 comma space 0 right parenthesis comma space straight P left parenthesis 4 comma space 4 right parenthesis

    From P. draw PM ⊥ x-axis.
    Required area = Area OAPB = Area OBPM - area OAPM
                            equals space integral subscript 0 superscript 4 square root of 4 straight x end root space dx space minus space integral subscript 0 superscript 4 straight x squared over 4 dx space equals space 2 integral subscript 0 superscript 4 straight x to the power of 1 half end exponent dx minus 1 fourth integral subscript 0 superscript 4 straight x squared dx space equals space 2 open square brackets fraction numerator straight x to the power of begin display style 3 over 2 end style end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript 4 minus 1 fourth open square brackets straight x cubed over 3 close square brackets subscript 0 superscript 4
equals space 2 space cross times space 2 over 3 open square brackets straight x to the power of 3 over 2 end exponent close square brackets subscript 0 superscript 4 space minus 1 fourth cross times 1 third open square brackets straight x cubed close square brackets subscript 0 superscript 4 space equals space 4 over 3 open square brackets open parentheses 4 close parentheses to the power of 3 over 2 end exponent minus 0 close square brackets space minus space 1 over 12 open square brackets left parenthesis 4 right parenthesis cubed minus 0 close square brackets
equals space 4 over 3 cross times 8 minus 1 over 12 cross times 64 space equals space 32 over 3 minus 16 over 3 equals space 16 over 3 space sq. space units.
    Now, the area of the region OAQBO bounded by curves straight y squared space equals 4 straight x and straight x squared space equals space 4 straight y

                                     equals space integral subscript 0 superscript 4 open parentheses 2 square root of straight x minus straight x squared over 4 close parentheses dx
equals space open square brackets 2 cross times 2 over 3 straight x to the power of 3 over 2 end exponent minus straight x cubed over 12 close square brackets subscript 0 superscript 4
equals space open square brackets 4 over 3 cross times 4 to the power of 3 over 2 end exponent minus fraction numerator left parenthesis 4 right parenthesis cubed over denominator 12 end fraction close square brackets space minus space left parenthesis 0 minus 0 right parenthesis
equals space 4 over 3 cross times 8 minus 16 over 3 equals 32 over 3 minus 16 over 3 equals 16 over 3 space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
    Again, the area of the region OPQAO bounded by the curves x2 = 4 y, x = 0, x = 4 and x-axis
    equals space integral subscript 0 superscript 4 straight x squared over 4 dx space equals space space 1 over 12 open square brackets straight x cubed close square brackets subscript 0 superscript 4
equals space 1 over 12 left parenthesis 4 cubed minus 0 right parenthesis space equals space 1 over 12 cross times 64 space equals space 16 over 3 space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis
    Similarly, the area of the region OBQRO bounded by the curve straight y squared space equals space 4 straight x comma space space straight y space equals space 0 space space and space space straight y space equals 4
    equals space integral subscript 0 superscript 4 space straight x space dy space equals space integral subscript 0 superscript 4 straight y squared over 4 dy space equals space 1 over 12 open square brackets straight y cubed close square brackets subscript 0 superscript 4 space equals space 16 over 3    ...(3)
    From (1), (2) and (3), it is clear that the area of the region OAQBO = area of the region OPQAO = area of the region OBQRO, i.e., urea bounded by parabolas y2 = 4 x and x2 = 4 y divides the area of the square in three equal parts.

    Question 87
    CBSEENMA12032824

    Write the order and degree of the differential equation
    open parentheses fraction numerator straight d squared straight y over denominator dx squared end fraction close parentheses squared plus open parentheses dy over dx close parentheses cubed plus 2 straight y space equals space 0

    Solution

    The given differential equation is
    open parentheses fraction numerator straight d squared straight y over denominator dx squared end fraction close parentheses squared plus open parentheses dy over dx close parentheses cubed plus 2 straight y space equals space 0
    Its order is 2 and degree is 2.

    Question 88
    CBSEENMA12032829

    Find the order and degrees, if defined, of each of the following differential equations:
    dy over dx minus cosx space equals 0

    Solution
    The given differential equation is dy over dx minus cosx space equals space 0.
    The highest order derivative present in the differential equation is dy over dx so its order is one. It is a  polynomial equation in dy over dx and the highest power raised to dy over dx is one, so its degree is one. 
    Question 89
    CBSEENMA12032830

    Find the order and degrees, if defined, of each of the following differential equations:
    straight x space straight y space fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight x open parentheses dy over dx close parentheses squared minus straight y dy over dx space equals space 0

    Solution
    The given differential equation is
    xy fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight x open parentheses dy over dx close parentheses squared minus straight y dy over dx equals 0
    The highest order derivative present in the given differential equation is fraction numerator straight d squared straight y over denominator dx squared end fraction. So its order is two. It is a polynomial  equation in fraction numerator straight d squared straight y over denominator dx squared end fraction space and space dy over dx and the highest power raised to fraction numerator straight d squared straight y over denominator dx squared end fraction is one, so its degree is one. 
    Question 90
    CBSEENMA12032831

    Find the order and degrees, if defined, of each the following differential equations:
    straight y to the power of straight m plus straight y squared plus straight e to the power of straight y space equals space 0

    Solution
    The given differential equation is
    straight y to the power of straight m plus straight y squared plus straight e to the power of straight y equals 0
    The highest order derivative present in the differential equation is y''', so its order is three. The given differential equation is not a polynomial equation in its derivative and so its degree is not defined.
    Question 91
    CBSEENMA12032832

    Determine order and degree (if defined) of differential equations:
    fraction numerator straight d to the power of 4 straight y over denominator dx to the power of 4 end fraction plus sin left parenthesis straight y to the power of straight m right parenthesis space equals space 0

    Solution
    The given differential equation is
    fraction numerator straight d to the power of 4 straight y over denominator dx to the power of 4 end fraction plus sin left parenthesis straight y to the power of straight m right parenthesis space equals space 0
    The highest order derivative present in the differential equation is fraction numerator straight d to the power of 4 straight y over denominator dx to the power of 4 end fraction
    ∴  its order is 4
    The given differential equation is not a polynomial equation in its derivative and so its degree is not defined.
    Question 92
    CBSEENMA12032833

    Determine order and degree (if defined) of differential equations:
    straight y apostrophe plus 5 space straight y equals 0

    Solution
    The given differential equation is
    y' + 5 y = 0
    The highest order derivative present in the given differential equation is y' and index of its highest power is one.
    ∴    the given differential equation is of order 1 and degree 1.
    Question 93
    CBSEENMA12032834

    Determine order and degree (if defined) of differential equations:
    open parentheses ds over dt close parentheses to the power of 4 plus 3 straight s fraction numerator straight d squared straight s over denominator dt squared end fraction equals 0


    Solution
    The given differential equation is
    open parentheses ds over dt close parentheses to the power of 4 plus 3 straight s fraction numerator straight d squared straight s over denominator dt squared end fraction equals space 0
    The highest order derivative present in the differential equation is fraction numerator straight d squared straight s over denominator dt squared end fraction
    ∴  its order is 2
    The highest power raised to fraction numerator straight d squared straight s over denominator dt squared end fraction is one, so its degree is 1.
    Question 94
    CBSEENMA12032835

    Determine order and degree (if defined) of differential equations:
    open parentheses fraction numerator straight d squared straight y over denominator dx squared end fraction close parentheses squared plus cos open parentheses dy over dx close parentheses space equals space 0



    Solution

    The given differential equation is
    open parentheses fraction numerator straight d squared straight y over denominator dx squared end fraction close parentheses squared plus cos open parentheses dy over dx close parentheses space equals space 0
    The highest order derivative present in the given differential equation is fraction numerator straight d squared straight y over denominator dx squared end fraction. therefore, its order is 2. Since the given differential equation is not a polynomial in dy over dx. therefore, its degree is not defined. 

    Question 95
    CBSEENMA12032836

    Determine order and degree (if defined) of differential equations:
    fraction numerator straight d squared straight y over denominator dx squared end fraction equals cos space 3 straight x plus space sin space 3 straight x




    Solution
    The given differential equation is
    fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space cos 3 straight x space plus space sin 3 straight x
    The highest order derivative present in the given differential equation is fraction numerator straight d squared straight y over denominator dx squared end fraction and index of its highest power is 1.
    ∴   the given differential equation is of order is 2 and degree 1.
    Question 96
    CBSEENMA12032837

    Determine order and degree (if defined) of differential equations:
    left parenthesis straight y to the power of straight m right parenthesis squared plus left parenthesis straight y to the power of straight m right parenthesis cubed plus left parenthesis straight y apostrophe right parenthesis to the power of 4 plus straight y to the power of 5 space equals space 0





    Solution
    The given differential equation is
    (y''')2 + (y'')3 + (y')4 + y5 = 0
    The highest order derivative present in the given differential equation is y''' and the index of its highest power is 2.
    ∴        the given differential equation is of order 3 and degree 2.
    Question 97
    CBSEENMA12032838

    Determine order and degree (if defined) of differential equations:
    straight y to the power of straight m plus 2 straight y to the power of straight n plus straight y apostrophe space equals space 0






    Solution
    The highest order derivative present in the given differential equation is y'" and the index of its highest power is 1.
    ∴   the given differential equation is of order 3 and degree 1.
    Question 98
    CBSEENMA12032839

    Determine order and degree (if defined) of differential equations:
    y' + y = ex






    Solution

    The given differential equation is
    y' + y = ex
    The highest order derivative present in the given differential equation is y' and the index of its highest power is 1.
    ∴     the given differential equation is of order 1 and degree 1.

    Question 99
    CBSEENMA12032840

    Determine order and degree (if defined) of differential equations:
    y'' + (y')2 + 2 y = 0




    Solution

    The given differential equation is
    y'' + (y')2 + 2 y = 0
    The highest order derivative present in the given differential equation is y' and the index of its highest power is 1.
    ∴  the given differential equation is of order 2 and degree 1.

    Question 100
    CBSEENMA12032841

    Determine order and degree (if defined) of differential equations:
    y″ + 2y′ + sin y = 0





    Solution

    The given differential equation is
    y'' + 2 y' + sin y = 0
    The highest order derivative present in the given differential equation, is y' and the index of its highest power is 1.
    ∴ the given differential equation is of order 2 and degree 1.

    Question 101
    CBSEENMA12032842

    For each of the differential equations given below, indicate its order and degree (if defined).
    fraction numerator straight d squared straight y over denominator dx squared end fraction plus 5 straight x open parentheses dy over dx close parentheses squared minus 6 straight y space equals space log space straight x


    Solution
    The given differential equation is
    fraction numerator straight d squared straight y over denominator dx squared end fraction plus 5 straight x open parentheses dy over dx close parentheses squared minus 6 straight y space equals space logx
    Since the order of the highest order derivative present in the given differential equation is 2.  therefore, its order is 2, Also, index of the highest power of  fraction numerator straight d squared straight y over denominator dx squared end fraction is one, therefore, degree of the given differential equation is 1.
    Question 102
    CBSEENMA12032844

    For each of the differential equations given below, indicate its order and degree (if defined).
    open parentheses dy over dx close parentheses cubed minus 4 open parentheses dy over dx close parentheses squared plus 7 straight y equals space sin space straight x


    Solution
    The given differential equation is
    open parentheses dy over dx close parentheses cubed minus 4 open parentheses dy over dxx close parentheses squared plus 7 straight y space equals space sin space straight x
    Since the highest order derivative present in the given differential equation is dy over dx comma therefore, order of the equation is 1. Also, index of the highest power of dy over dx is 3. So degree is 3.
    Question 103
    CBSEENMA12032847

    For each of the differential equations given below, indicate its order and degree (if defined).
    fraction numerator straight d to the power of 4 straight y over denominator dx to the power of 4 end fraction minus sin open parentheses fraction numerator straight d cubed straight y over denominator dx cubed end fraction close parentheses space equals 0



    Solution
    The given differential equation is
    fraction numerator straight d to the power of 4 straight y over denominator dx to the power of 4 end fraction minus sin open parentheses fraction numerator straight d cubed straight y over denominator dx cubed end fraction close parentheses space equals space 0
    Since the highest order derivative present in the given differential equation is fraction numerator straight d to the power of 4 straight y over denominator dx to the power of 4 end fraction comma therefore, order of the equation is 4. As sin space open parentheses fraction numerator straight d cubed straight y over denominator dx cubed end fraction close parentheses occurs in the equation, therefore, degree of the given equation is not defined. 
    Question 104
    CBSEENMA12032852

    Find the order and degree of the differential equation straight x dy over dx plus fraction numerator 3 over denominator begin display style dy over dx end style end fraction equals straight y squared state also if this is linear or non-linear. 

    Solution

    The given differential equation is
                    straight x dy over dx plus fraction numerator 3 over denominator begin display style dy over dx end style end fraction equals straight y squared
    or   straight x open parentheses dy over dx close parentheses squared plus 3 space equals space straight y squared dy over dx
    or    straight x open parentheses dy over dx close parentheses squared minus straight y squared dy over dx plus 3 space equals space 0
    It is of order 1, degree 2 and non-linear.

    Question 105
    CBSEENMA12032854

    Find the order and degree of the equation y = px + square root of straight a squared straight p squared plus straight b squared end root when straight p space equals space dy over dx.
    State also if this is linear or non-linear.

    Solution

    The given equation is
                    straight y equals px plus square root of straight a squared straight p squared plus straight b squared end root space space space or space space space space space space space straight y minus straight p space straight x space space equals square root of straight a squared straight p squared plus straight b squared end root
    or             left parenthesis straight y minus px right parenthesis squared space equals straight a squared straight p squared plus straight b squared      or       straight y squared plus straight p squared straight x squared space minus space 2 space pxy space equals straight a squared straight p squared plus straight b squared
    or            straight y squared plus straight x squared open parentheses dy over dx close parentheses squared minus 2 xy dy over dx space equals space straight a squared open parentheses dy over dx close parentheses squared plus straight b squared
    It is of order 1, degree 2 and non-linear

    Question 106
    CBSEENMA12032856

    Determine the order and degree of the differential equation:
    open square brackets 1 plus open parentheses dy over dx close parentheses squared close square brackets to the power of 3 over 2 end exponent space equals 5 fraction numerator straight d squared straight y over denominator dx squared end fraction

    Solution
    The given differential equation is
                                 open square brackets 1 plus open parentheses dy over dx close parentheses squared close square brackets to the power of 3 over 2 end exponent space equals space 5 fraction numerator straight d squared straight y over denominator dx squared end fraction
    This can be written as
                                       open square brackets 1 plus open parentheses dy over dx close parentheses squared close square brackets to the power of 3 over 2 end exponent space equals space 25 open parentheses fraction numerator straight d squared straight y over denominator dx squared end fraction close parentheses squared
    ∴ degree of differential equation is 2 and order 2.
    Question 107
    CBSEENMA12032858

    Determine the order and degree of the differential equation:
    square root of straight x fraction numerator straight d to the power of 4 straight y over denominator dx to the power of 4 end fraction plus 5 open parentheses dy over dx close parentheses squared space equals 2 straight y squared minus straight x

    Solution

    The given differential equation is
    square root of straight x fraction numerator straight d to the power of 4 straight y over denominator dx to the power of 4 end fraction plus 5 open parentheses dy over dx close parentheses squared space equals 2 straight y squared minus straight x
    Here highest differential coefficient is  fraction numerator straight d to the power of 4 straight y over denominator dx to the power of 4 end fraction and its degree is one.
    ∴   order of given differential equation is 4 and degree 1.

    Question 108
    CBSEENMA12032859

    The degree of the differential equation open parentheses fraction numerator straight d squared straight y over denominator dx squared end fraction close parentheses cubed plus open parentheses dy over dx close parentheses squared plus sin open parentheses dy over dx close parentheses plus 1 space space equals space 0 is
    • 3

    • 2

    • 1

    • not defined

    Solution

    D.

    not defined

    The given differential equation is open parentheses fraction numerator straight d squared straight y over denominator dx squared end fraction close parentheses cubed plus open parentheses dy over dx close parentheses squared plus sin open parentheses dy over dx close parentheses plus 1 space equals space 0
    Since the differential equation is not a polynomial equation in its derivatives
    ∴   its degree is not defined
    Question 109
    CBSEENMA12032860

    The degree of the differential equation 2 straight x squared fraction numerator straight d squared straight y over denominator dx squared end fraction minus 3 dy over dx plus straight y space equals space 0  is
    • 2

    • 1

    • 0

    • not defined

    Solution

    A.

    2

    The given differential equation is 2 straight x squared fraction numerator straight d squared straight y over denominator dx squared end fraction minus 3 dy over dx plus straight y space equals 0
    The highest order derivative present in the differential equation is fraction numerator straight d squared straight y over denominator dx squared end fraction.
    ∴   its order is 2

    Question 110
    CBSEENMA12032862
    Question 111
    CBSEENMA12032863

    Verify that the function y = a cos x + b sin x, where a, b ∊ R is a solution of the differential equation fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight y space equals space 0.

    Solution

                              straight y space equals space straight a space cosx space plus space straight b space sinx                          ...(1)
               therefore space space space dy over dx space equals space minus straight a space sinx space plus space straight b space cosx
rightwards double arrow space space space space fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space minus straight a space cosx space minus space straight b space sinx
rightwards double arrow space space space fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space minus straight y space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space space of space left parenthesis 1 right parenthesis close square brackets
rightwards double arrow space fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight y space equals space 0
    therefore space space space straight y space equals space straight a space cosx space plus space straight b space sinx is a solution of the differential equation
                          fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight y space equals space 0.

    Question 112
    CBSEENMA12032865

    Verify that y - 3 cos (log x) + 4 sin (log x) is a solution of the differential equation straight x squared fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight x dy over dx plus straight y space equals space 0.

    Solution

                           straight y space equals space 3 space cos space left parenthesis log space straight x right parenthesis space plus space 4 space sin space left parenthesis log space straight x right parenthesis               ...(1)
    therefore space space space dy over dx equals 3 space sin space left parenthesis log space straight x right parenthesis. space space 1 over straight x plus 4 space cos space left parenthesis log space straight x right parenthesis. space 1 over straight x
therefore space space space straight x dy over dx equals negative 3 space sin space left parenthesis log space straight x right parenthesis space plus space 4 space cos thin space left parenthesis log space straight x right parenthesis
    Again differentiating w.r.t.x, we get,
                   straight x fraction numerator straight d squared straight y over denominator dx squared end fraction plus dy over dx.1 space equals space minus 3 space cos space left parenthesis log space straight x right parenthesis. space 1 over straight x minus space 4 space sin space left parenthesis log space straight x right parenthesis. space 1 over straight x
    therefore space space space space straight x squared fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight x dy over dx space equals space minus 3 space cos space left parenthesis log space straight x right parenthesis space minus space space 4 space sin space left parenthesis log space straight x right parenthesis
therefore space space space space space straight x squared fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight x dy over dx equals space space minus straight y space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
therefore space space space space space straight x squared fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight x dy over dx plus straight y space equals space 0
    therefore space space space space straight y space equals space 3 space cos space left parenthesis log space straight x right parenthesis space plus space 4 space sin space left parenthesis log space straight x right parenthesis is a solution of the differential equation
                           straight x squared fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight x dy over dx plus straight y space equals space 0.

    Question 113
    CBSEENMA12032868

    Verify that the function y = e–3x is a solution of the differential equation fraction numerator straight d squared straight y over denominator dx squared end fraction plus dy over dx minus 6 straight y space equals space 0

    Solution

                      straight y space equals space straight e to the power of negative 3 straight x end exponent                                                                      ...(1)
    therefore         dy over dx space equals space straight e to the power of negative 3 straight x end exponent. space left parenthesis negative 3 right parenthesis space space space space space space space or space space space space space dy over dx equals negative 3 straight e to the power of negative 3 straight x end exponent                ...(2)
             fraction numerator straight d squared straight y over denominator dx squared end fraction equals negative 3 space straight e to the power of negative 3 straight x end exponent. space left parenthesis negative 3 right parenthesis space space space or space space space fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space 9 straight e to the power of negative 3 straight x end exponent                  ...(3)
    L.H.S. = fraction numerator straight d squared straight y over denominator dx squared end fraction plus dy over dx minus 6 straight y space equals space 9 straight e to the power of negative 3 straight x end exponent minus 3 straight e to the power of 3 straight x end exponent minus 6 straight e to the power of negative 3 straight x end exponent space space space space space open square brackets because space of space left parenthesis 1 right parenthesis comma space left parenthesis 2 right parenthesis comma space left parenthesis 3 right parenthesis close square brackets
                = 0 - R.H.S.
    therefore space space space straight y space equals straight e to the power of negative 3 straight x end exponent  is a solution of the differential equation
                            fraction numerator straight d squared straight y over denominator dx squared end fraction plus dy over dx minus 6 straight y space equals space 0

    Question 114
    CBSEENMA12032871

    Show that the function y = ae2X + be–x is a solution of differential equation fraction numerator straight d squared straight y over denominator dx squared end fraction minus dy over dx minus 2 straight y space equals space 0.

    Solution

    Here straight y space equals space straight a space straight e to the power of 2 straight x end exponent plus straight b space straight e to the power of straight x                                                ...(1)
    therefore space space space space dy over dx space equals space ae to the power of 2 straight x end exponent. space 2 space plus space straight b space straight e to the power of negative straight x end exponent left parenthesis negative 1 right parenthesis space space space space space space rightwards double arrow space space space space dy over dx space equals space 2 space straight a space straight e to the power of 2 straight x end exponent space minus space straight b space straight e to the power of negative straight x end exponent    ...(2)
    Again differentiating w.r.t. x, we get,
                                 fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space 4 space straight a space straight e to the power of 2 straight x end exponent plus straight b space straight e to the power of straight x                                                  ...(3)
    L.H.S. = fraction numerator straight d squared straight y over denominator dx squared end fraction space minus dy over dx minus 2 straight y               
               equals space 4 space straight a space straight e to the power of 2 straight x end exponent plus space straight b space straight e to the power of straight x space minus space 2 space straight a space straight e to the power of 2 straight x end exponent plus space straight b space straight e to the power of negative straight x end exponent minus 2 space straight a space straight e to the power of 2 straight x end exponent minus space 2 space straight b space straight e to the power of negative straight x end exponent space space space space left square bracket because space of space left parenthesis 1 right parenthesis comma space left parenthesis 2 right parenthesis comma space left parenthesis 3 right parenthesis right square bracket
                 equals space 0 space equals space straight R. straight H. straight S.
    therefore space space space straight y space equals space straight a space straight e to the power of 2 straight x end exponent plus straight b space straight e to the power of straight x is a solution of the differential equation
                      fraction numerator straight d squared straight y over denominator dx squared end fraction minus dy over dx minus 2 straight y space equals space 0

    Question 115
    CBSEENMA12032873

    In the following, verify that the given functions, (explicit or implicit) is a solution of the corresponding differential equation:
    straight y space equals space straight e to the power of straight x plus 1                    :    straight y to the power of straight n minus straight y apostrophe space equals space 0

    Solution

    y = ex + 1 ;   ...(1)
    ∴ y' = ex    ...(2)
    and    y'' = ex    ...(3)
    L.H.S. = y'' – y'
    = ex – ex    [∵ of (2), (3)]
    = 0 = R.H.S.
    ∴ y = ex + 1 is a solution of y'' – y' = 0

    Question 116
    CBSEENMA12032874
    Question 118
    CBSEENMA12032877

    In the following, verify that the given functions, (explicit or implicit) is a solution of the corresponding differential equation:
    straight y space equals space square root of 1 plus straight x squared end root               :   straight y apostrophe space equals space fraction numerator xy over denominator 1 plus straight x squared end fraction

    Solution

                   straight y space equals space square root of 1 plus straight x squared end root                                                      ...(1)
    therefore          straight y apostrophe space equals space fraction numerator 2 straight x over denominator 2 square root of 1 plus straight y squared end root end fraction space space or space space space straight y apostrophe space equals space fraction numerator straight x over denominator square root of 1 plus straight x squared end root end fraction               ...(2)
            R.H.S. = fraction numerator xy over denominator 1 plus straight x squared end fraction space equals space fraction numerator straight x square root of 1 plus straight x squared end root over denominator 1 plus straight x squared end fraction                            open square brackets because space space of space space left parenthesis 1 right parenthesis close square brackets
                       equals space fraction numerator straight x over denominator square root of 1 plus straight x squared end root end fraction space equals straight y apostrophe                                        open square brackets because space of space left parenthesis 2 right parenthesis close square brackets
                       equals space straight L. straight H. straight S.
    therefore space space space straight y space equals space square root of 1 plus straight x squared end root is a solution of straight y apostrophe space equals space fraction numerator xy over denominator 1 plus straight x squared end fraction
                   

    Sponsor Area

    Question 121
    CBSEENMA12032883

    In the following, verify that the given functions, (explicit or implicit) is a solution of the corresponding differential equation:
    straight y minus cos space straight y space equals space straight x  :         left parenthesis straight y space sin space straight y space plus space cos space straight y space plus space straight x right parenthesis space straight y apostrophe space equals space straight y                                          

    Solution

    y – cos y = x    ...(1)
    Differentiate both sides w.r.t. x, we get,
    y' + sin y . y' = 1
    ⇒ y'(1 + sin y) = 1    ...(2)
    L.H.S. = (y sin y + cos y + x) y'
    = (y sin y + y) y'    [∵ of (1)]
    = y (1 + sin y) y' = y. 1    [∵ of(2)]
    = y
    = R.H.S.
    ∴ y – cos y = x is a solution of (y sin y + cos y + x) y' = y.

    Question 123
    CBSEENMA12032886

    In the following, verify that the given functions, (explicit or implicit) is a solution of the corresponding differential equation:
    straight y space equals space square root of straight a squared minus straight x squared end root space comma space straight x space element of space left parenthesis negative straight a comma space straight a right parenthesis space colon space space space space space space straight x plus straight y space dy over dx space equals space 0 space space space left parenthesis straight y not equal to 0 right parenthesis
                                                      

    Solution

                             straight y space equals space square root of straight a squared minus straight x squared end root                                     ...(1)
    therefore space                  straight y apostrophe space equals space fraction numerator negative 2 straight x over denominator 2 square root of straight a squared minus straight x squared end root end fraction
    rightwards double arrow space space space space straight y apostrophe equals negative fraction numerator straight x over denominator square root of straight a squared minus straight x squared end root end fraction
    rightwards double arrow space space space space space space space space space dy over dx equals negative straight x over straight y space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
rightwards double arrow space space space space space space straight y dy over dx space equals space minus straight x
rightwards double arrow space space space space straight x plus straight y dy over dx space equals space 0 space
therefore space space space straight y space equals space square root of straight a squared minus straight x squared end root space is space straight a space solution space of space straight x plus straight y dy over dx space equals space 0.

    Question 124
    CBSEENMA12032891
    Question 125
    CBSEENMA12032893

    For problem given below, verify that the given function (implicit or explicit) is a solution of the corresponding differential equation:straight y equals straight e to the power of straight x left parenthesis straight a space cosx space plus space straight b space sin space straight x right parenthesis space colon thin space fraction numerator straight d squared straight y over denominator dx squared end fraction minus 2 dy over dx plus 2 straight y space equals space 0
             

    Solution

    The given differential equation is
    y = ex (a cos x + b sin x)
    ⇒    e–x y = a cos x + b sin x    ...(1)
    Differentiating (1) twice w.r.t. .x. we get
                      straight e to the power of negative straight x end exponent dy over dx plus straight y space straight e to the power of negative straight x end exponent left parenthesis negative 1 right parenthesis space equals space minus straight a space sinx space plus space straight b space cosx
    and        straight e to the power of negative straight x end exponent fraction numerator straight d squared straight y over denominator dx squared end fraction plus dy over dx straight e to the power of negative straight x end exponent left parenthesis negative 1 right parenthesis minus open curly brackets negative ye to the power of negative straight x end exponent plus straight e to the power of negative straight x end exponent dy over dx close curly brackets space equals space minus straight a space cosx space minus space straight b space sinx
    or            straight e to the power of negative straight x end exponent fraction numerator straight d squared straight y over denominator dx squared end fraction minus 2 straight e to the power of negative straight x end exponent dy over dx plus straight y space straight e to the power of negative straight x end exponent space equals space minus straight y space straight e to the power of negative straight x end exponent                     [because space of space left parenthesis 1 right parenthesis]
    or         straight e to the power of negative straight x end exponent fraction numerator straight d squared straight y over denominator dx squared end fraction minus 2 straight e to the power of negative straight x end exponent dy over dx plus 2 space straight y space straight e to the power of negative straight x end exponent space equals space 0 space space or space space straight e to the power of negative straight x end exponent open curly brackets fraction numerator straight d squared straight y over denominator dx squared end fraction minus 2 dy over dx plus 2 straight y close curly brackets space equals space 0
    or            fraction numerator straight d squared straight y over denominator dx squared end fraction minus 2 dy over dx plus 2 straight y space equals space 0
    Hence the result. 

    Question 126
    CBSEENMA12032896

    For problem given below, verify that the given function (implicit or explicit) is a solution of the corresponding differential equation:
    straight y space equals space straight x space sin space 3 straight x             :    fraction numerator straight d squared straight y over denominator dx squared end fraction plus 9 straight y minus 6 space cos space 3 straight x space equals space 0
             

    Solution
    The given differential equation is
                        straight y equals space straight x space sin space 3 straight x                       ...(1)
     rightwards double arrow         dy over dx space equals space straight x space cos 3 straight x space. space 3 space plus space sin space 3 straight x
    and    fraction numerator straight d squared straight y over denominator dx squared end fraction equals 3 space open curly brackets straight x left parenthesis negative sin space 3 straight x space.3 right parenthesis plus cos space 3 straight x close curly brackets space plus space cos space 3 straight x. space 3
    or     fraction numerator straight d squared straight y over denominator dx squared end fraction equals negative 9 space straight x space sin 3 straight x space plus space 6 space cos space 3 straight x
    or      fraction numerator straight d squared straight y over denominator dx squared end fraction equals negative 9 straight y plus 6 space cos space 3 straight x                       open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
    or   fraction numerator straight d squared straight y over denominator dx squared end fraction plus 9 straight y minus 6 space cos space 3 straight x space equals space 0.
    Hence the result. 
    Question 127
    CBSEENMA12032899

    For problem given below, verify that the given function (implicit or explicit) is a solution of the corresponding differential equation:
    straight x squared space equals space 2 straight y squared space log space straight y    :     left parenthesis straight x squared plus straight y squared right parenthesis space dy over dx minus straight x space straight y space equals space 0
       

    Solution
    The given differential equation is
                                straight x squared space equals space 2 straight y squared log space straight y                 ...(1)
    therefore space space space space space         2 straight x space equals space 2 open curly brackets straight y squared cross times 1 over straight y dy over dx plus space log space straight y space open parentheses 2 space straight y space dy over dx close parentheses close curly brackets
    or                  2 straight x space equals 2 left parenthesis straight y plus 2 space straight y space log space straight y right parenthesis dy over dx
    rightwards double arrow               straight x equals left parenthesis straight y plus 2 space straight y space log space straight y right parenthesis dy over dx
    Multiplying both sides by y, we get
                                    straight x space straight y space equals space left parenthesis straight y squared plus 2 straight y squared space log space straight y right parenthesis dy over dx
    or                            xy space equals space left parenthesis straight y squared plus straight x squared right parenthesis space dy over dx                   open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
    or          left parenthesis straight x squared plus straight y squared right parenthesis space dy over dx minus straight x space straight y space equals space 0
    Hence the result. 
    Question 128
    CBSEENMA12032901

    The number of arbitrary constants in the general solution of a differential equation of fourth order are:
    • 0

    • 2

    • 3

    • 4

    Solution

    D.

    4

    Since the number of arbitrary constants in the general solution of a differential equation of nth order is n.
    Question 129
    CBSEENMA12032902

    The number of arbitrary constants in the particular solution of a differential equation of third order are
    • 3

    • 2

    • 1

    • 0

    Solution

    D.

    0

    Since there is no arbitrary constant in particular solution.
    ∴    (D) is correct answer.
    Question 130
    CBSEENMA12032905

    Find the differential equation that will represent the family of straight lines y = m x + c, where m, c (∈ R) are parameters.

    Solution

    The equation of the family of lines is
                          y = mx + c
    therefore space space space space space space space space space dy over dx space equals space straight m
    Again differentiating w.r.t. 'x' we get, 
    fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space 0
    This is required differential equations.

    Question 131
    CBSEENMA12032906

    Find the differential equations from y = k esin–1 x   + 3.

    Solution

    The given equation is straight y space equals space ke to the power of sin to the power of negative 1 end exponent straight x end exponent plus 3                ...(1)
    therefore space space space dy over dx equals space straight k space straight e to the power of sin to the power of negative 1 end exponent straight x end exponent. fraction numerator 1 over denominator square root of 1 minus straight x squared end root end fraction space or space space dy over dx space equals space left parenthesis straight y minus 3 right parenthesis. space fraction numerator 1 over denominator square root of 1 minus straight x squared end root end fraction space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
    or space space square root of 1 minus straight x squared end root space dy over dx equals straight y minus 3 comma space which is required differential equation.

    Question 132
    CBSEENMA12032909

    Represent the following family of curves by forming the corresponding differential equations (a. b: parameters).
    straight x squared plus straight y squared space space equals space straight a squared

    Solution
    The equation of curve is
    x2 + y2 = a2
    Differentiating both sides w.r.t. x, we get,
    2 straight x plus 2 straight y space dy over dx space equals space 0             or           straight x plus straight y dy over dx equals 0
    which is required differential equation. 
    Question 133
    CBSEENMA12032910

    Represent the following family of curves by forming the corresponding differential equations (a. b: parameters).
    straight x squared minus straight y squared space equals space straight a squared

    Solution
    The equation of curve is
    x2 – y2 = a2
    Differentiating both sides w.r.t. x,
    2 straight x minus 2 straight y dy over dx equals 0   or      straight x minus straight y dy over dx equals 0
    which is required differential equation.
    Question 134
    CBSEENMA12032912

    Represent the following family of curves by forming the corresponding differential equations (a. b: parameters).
    straight y squared equals 4 ax

    Solution
    The equation of curve is
    y2 = 4 a x    ...(1)
    Differentiating both sides w.r.t x, we get.
                       2 straight y dy over dx space equals space 4 straight a          ...(2)
    From (1) and (2), we get,
                      straight y squared space equals space 2 straight y space dy over dx. straight x space space space space space space space or space space space space straight y space equals space 2 straight x dy over dx
    Which is required differential equation.
    Question 135
    CBSEENMA12032913

    Represent the following family of curves by forming the corresponding differential equations (a. b: parameters).
    left parenthesis straight x minus straight a right parenthesis squared minus straight y squared space equals space 1

    Solution

    The equation of given curve is
    (x – a)2 – y2 = 1    ...(1)
    Differentiating both sides w.r.t x, we get.
    2 left parenthesis straight x minus straight a right parenthesis minus 2 straight y dy over dx equals 0                 or             straight x minus straight a space equals space straight y dy over dx
    Putting value of x – a in (1), we get,
    straight y squared open parentheses dy over dx close parentheses squared minus straight y squared space equals space 1
    which is required differential equation.

    Question 136
    CBSEENMA12032915

    Represent the following family of curves by forming the corresponding differential equations (a. b: parameters).
    straight x over straight a plus straight y over straight b equals 1


    Solution
    The equation of given curve is
    straight x over straight a plus straight y over straight b equals 1
    Differential w.r.t x, we get,
    1 over straight a plus 1 over straight b dy over dx equals 0
    Again differentiating w.r.t x, we get.
    0 plus 1 over straight b fraction numerator straight d squared straight y over denominator dx squared end fraction equals 0                       rightwards double arrow space space space space fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space 0
    which is required differential equation.
    Question 137
    CBSEENMA12032918

    Represent the following family of curves by forming the corresponding differential equations (a. b: parameters).
    straight x squared over straight a squared plus straight y squared over straight b squared space equals space 1



    Solution

    The equation of curve is
               straight x squared over straight a squared plus straight y squared over straight b squared space equals space 1                          ...(1)
    Differentiating w.r.t., x successively two times, we get.
             fraction numerator 2 straight x over denominator straight a squared end fraction plus fraction numerator 2 yy subscript 1 over denominator straight b squared end fraction equals 0   or     straight x over straight a squared plus fraction numerator straight y space straight y subscript 1 over denominator straight b squared end fraction equals 0           ...(2)
    rightwards double arrow space space space space space space space space space space space straight a squared over straight b squared equals space minus fraction numerator straight x over denominator straight y space straight y subscript 1 end fraction                                              ...(3)
    and  1 over straight a squared plus fraction numerator straight y space straight y subscript 2 space plus space straight y subscript 1 superscript 2 over denominator space straight b squared end fraction space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space rightwards double arrow space space space straight a squared over straight b squared space equals space fraction numerator negative 1 over denominator straight y space straight y subscript 2 space plus space straight y subscript 1 squared end fraction     ...(4)
    From (3), (4), we get, 
                           fraction numerator negative straight x over denominator straight y space straight y subscript 1 end fraction space equals space fraction numerator negative 1 over denominator straight y space straight y subscript 2 space plus space straight y subscript 1 squared end fraction space space space space space space rightwards double arrow space space space space straight x space left parenthesis straight y space straight y subscript 2 plus space straight y subscript 1 squared right parenthesis space minus space straight y space straight y subscript 1 space equals space 0
    which is the required differential equation. 

    Question 138
    CBSEENMA12032920

    Represent the following family of curves by forming the corresponding differential equations (a. b: parameters).
    straight x squared over straight a squared minus straight y squared over straight b squared space equals space 1




    Solution
    The general equation of hyperbolas is
    straight x squared over straight a squared minus straight y squared over straight b squared equals 1                             ...(1)
    Differentiating w.r.t., x successively two times, we get,
                      fraction numerator 2 straight x over denominator straight a squared end fraction minus fraction numerator 2 space straight y space straight y subscript 1 over denominator straight b squared end fraction space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space rightwards double arrow space space space straight x over straight a squared minus fraction numerator straight y space straight y subscript 1 over denominator straight b squared end fraction space equals space 0
    rightwards double arrow space space space space space space space space space space space space space space space straight a squared over straight b squared space equals space fraction numerator straight x over denominator straight y space straight y subscript 1 end fraction                ...(2)
    and   1 over straight a squared minus fraction numerator straight y space straight y subscript 2 space plus space straight y subscript 1 squared over denominator straight b squared end fraction space equals space 0 space space space space space space space space space space space space space space space space space space space rightwards double arrow space space space space straight a squared over straight b squared space equals space fraction numerator 1 over denominator straight y space straight y subscript 2 space plus space straight y subscript 1 squared end fraction    ...(3)
    From (2), (3), we get,
                                fraction numerator straight x over denominator straight y space straight y subscript 1 end fraction space equals space fraction numerator 1 over denominator straight y space straight y subscript 2 plus space straight y subscript 1 squared end fraction space space space space or space space space straight x space left parenthesis straight y space straight y subscript 2 space plus space straight y subscript 1 squared right parenthesis space minus space straight y space straight y subscript 1 space equals space 0
    which is the required differential equation.
    Question 139
    CBSEENMA12032922

    Represent the following family of curves by forming the corresponding differential equations (a. b: parameters).
    straight y squared minus 4 straight a left parenthesis straight x minus straight b right parenthesis





    Solution

    The equation of given curve is
    y2 = 4 a (x – b)
    Differentiating w.r.t. x, we get,
    2 straight y dy over dx space equals space 4 space straight a                or   straight y dy over dx space equals 2 straight a
    Again differentiating w.r.t x, we get.
    straight y fraction numerator straight d squared straight y over denominator dx squared end fraction plus dy over dx. dy over dx space equals space 0       or   straight y fraction numerator straight d squared straight y over denominator dx squared end fraction plus open parentheses dy over dx close parentheses squared space equals space 0
    which is required differential equation..

    Question 140
    CBSEENMA12032924

    Represent the following family of curves by forming the corresponding differential equations (a. b: parameters).
    left parenthesis straight y minus straight b right parenthesis squared space equals space 4 left parenthesis straight x minus straight a right parenthesis






    Solution

    The equation of given curve is
                                       left parenthesis straight x minus straight b right parenthesis squared space space equals space 4 left parenthesis straight x minus straight a right parenthesis                           ...(1)
             Differentiating w.r.t.x, we get, 
                         2 left parenthesis straight y minus straight b right parenthesis dy over dx space equals space 4     or    left parenthesis straight y minus straight b right parenthesis space dy over dx equals 2       ....(2)
    Again differentiating both sides w.r.t x we get,
             left parenthesis straight y minus straight b right parenthesis fraction numerator straight d squared straight y over denominator dx squared end fraction plus dy over dx. dy over dx space space equals space 0 space space space space space or space space space fraction numerator 2 over denominator begin display style dy over dx end style end fraction fraction numerator straight d squared straight y over denominator dx squared end fraction plus open parentheses dy over dx close parentheses squared space equals space 0   open square brackets because space of space left parenthesis 2 right parenthesis close square brackets
    or           2 fraction numerator straight d squared straight y over denominator dx squared end fraction plus open parentheses dy over dx close parentheses cubed space equals space 0 comma which is required differential equation. 
                                       

    Question 141
    CBSEENMA12032925

    Represent the following family of curves by forming the corresponding differential equations (a. b: parameters).
    straight x squared plus straight y squared space equals space 2 ax







    Solution

    The given equation is
                           straight x squared plus straight y squared space equals space 2 ax                    ...(1)
    Differentiating both sides w.r.t. x, we get,
                         2 straight x plus 2 straight y dy over dx space equals space 2 straight a               ...(2)
    Putting value of 2a from (2) in (1), we get,
                            straight x squared plus straight y squared space equals space open parentheses 2 straight x plus 2 straight y dy over dx close parentheses straight x
    or            straight x squared plus straight y squared space equals space 2 straight x squared plus 2 xy dy over dx space space space space or space space space 2 xy dy over dx plus straight x squared minus straight y squared space equals space 0
    which is the required differential equation.

    Question 142
    CBSEENMA12032926

    Find the differential equation that will represent the family of curves given by (a, b: parameter):
    y = ax3

    Solution
    The given equation is
    y = ax3                                       ...(1)
         dy over dx space equals space 3 ax squared                        ...(2)
    Dividing (1) by (2), we get
                         fraction numerator straight y over denominator begin display style dy over dx end style end fraction space equals straight x over 3                 or        straight x dy over dx space equals space 3 straight y
     which is required differential equation
    Question 143
    CBSEENMA12032927

    Find the differential equation that will represent the family of curves given by (a, b: parameter):
    x2 + y2 = a x3

    Solution
    The given differential equation is
                        straight x squared plus straight y squared space equals space ax cubed                             ...(1)
                2 straight x plus 2 straight y dy over dx space equals 3 ax squared                           ...(2)
    Multiply (1) by 3 and (2) by x, we get,
                        3 straight x squared plus 3 straight y squared space equals space 3 ax cubed                     ...(3)
                  2 straight x squared plus 2 xy dy over dx space equals space 3 ax cubed                    ...(4)
    Subtracting (4) from (3), we get
                     straight x cubed plus 3 straight y squared minus 2 xy dy over dx equals 0
    or             straight x squared plus 3 straight y squared equals 2 xy dy over dx
    which is required differential equation.
    Question 144
    CBSEENMA12032928

    Find the differential equation that will represent the family of curves given by (a, b: parameter):
    y = eax

    Solution
    The given differential equation is
                                 straight y equals straight e to the power of ax space space space space space space space space space space space space space space space space space space space space space space space space space space space or space space space space log space straight y space equals space log space straight e to the power of ax
    therefore space space space space space space space log space straight y space space equals space straight a space straight x                                                             ...(1)
    Differentiating w.r.t. x, we get,
                       1 over straight y dy over dx equals straight a                                                       ...(2)
    From (1) and (2), we get,
                            log space straight y space equals space 1 over straight y dy over dx. straight x             or   straight x dy over dx space equals space straight y space log space straight y
    which is required differential equation.
    Question 145
    CBSEENMA12032931

    Form the differential equation corresponding to y2 – 2 a y + x2 – a2 by eliminating a. 

    Solution
    The given equation is
                                      straight y squared minus 2 ay plus straight x squared space equals space straight a squared               ...(1)
    Differentiating both sides w.r.t.x, we get, 
                      2 space straight y space dy over dx minus 2 space straight a dy over dx plus 2 straight x equals 0 space space space or space space straight y dy over dx plus straight x space equals space straight a dy over dx
    therefore space space space straight a space equals space fraction numerator straight y begin display style dy over dx end style plus straight x over denominator begin display style dy over dx end style end fraction                                                 ...(2)
    Eliminating m from (1) and (2), we get,
         straight y squared minus fraction numerator 2 straight y squared begin display style dy over dx end style plus 2 xy over denominator begin display style dy over dx end style end fraction plus straight x squared space equals space open parentheses straight y begin display style dy over dx end style plus straight x close parentheses squared over open parentheses begin display style dy over dx end style close parentheses squared
    or        open parentheses straight x squared plus straight y squared close parentheses open parentheses dy over dx close parentheses squared minus 2 straight y squared open parentheses dy over dx close parentheses squared minus 2 xy open parentheses dy over dx close parentheses space equals space open parentheses straight y dy over dx plus straight x close parentheses squared
    or          open parentheses straight x squared plus straight y squared close parentheses open parentheses dy over dx close parentheses squared minus 2 straight x squared open parentheses dy over dx close parentheses squared minus 2 xy dy over dx equals straight y squared open parentheses dy over dx close parentheses squared plus straight x squared plus 2 xy dy over dx
    or           open parentheses straight x squared minus 2 straight y squared close parentheses space open parentheses dy over dx close parentheses squared space minus space 4 xy dy over dx minus straight x squared space equals space 0
    or        left parenthesis 2 straight y squared minus straight x squared right parenthesis space open parentheses dy over dx close parentheses squared plus 4 xy dy over dx plus straight x squared space equals space 0
    which is required differential equation. 
    Question 146
    CBSEENMA12032932

    Form the differential equation representing the family of curves y = a sin (x + b), where a and b are arbitrary constants.  

    Solution
    The given equation is
                            y = a sin (x + b)                          ...(1)
     Differentiating w.r.t.x, we get,
                             dy over dx space equals space straight a space cos left parenthesis straight x plus straight b right parenthesis
    Again differentiating w.r.t.x, we get,
                                fraction numerator straight d squared straight y over denominator dx squared end fraction space equals negative asin left parenthesis straight x plus straight b right parenthesis
    or               fraction numerator straight d squared straight y over denominator dx squared end fraction equals space minus straight y                                  open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
    or               fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight y space equals space 0
     which is required differential equation.
    Question 147
    CBSEENMA12032933

    Form the differential equation representing the family of curves y = a cos (x + b) where a and b are arbitrary constants.

    Solution

    The given equation is straight y space equals space straight a space cos left parenthesis straight x plus straight b right parenthesis               ...(1)
    Differentiating w.r.t.x, we get,   dy over dx equals negative straight a space sin left parenthesis straight x plus straight b right parenthesis
    Again differentiating w.r.t. x, we get, 
                         fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space minus straight a space cos space left parenthesis straight x plus straight b right parenthesis space space space space space space or space space space space space fraction numerator straight d squared straight y over denominator dx squared end fraction equals negative straight y space space space space space space space space space space left square bracket because space space of space left parenthesis 1 right parenthesis right square bracket
    or              fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight y space equals space 0
    which is required differential equation.

    Question 148
    CBSEENMA12032935

    Find the differential equation of the family of curves  y = A sin mx + B cos mx. where m is fixed, and A and B are arbitrary constants.

    Solution

    The given equation is
                y = A sin mx + B cos mx.                               ...(1)
    therefore space space space dy over dx equals space straight m space straight A space sin space mx space plus space straight m space straight B space cos space mx
    rightwards double arrow space space fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space straight m squared straight A space cos space mx space minus space straight m squared space straight B space sin space mx
rightwards double arrow space space space fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space minus straight m squared left parenthesis straight A space cos space mx space plus space straight B space sin space mx right parenthesis
rightwards double arrow space space space fraction numerator straight d squared straight y over denominator dx squared end fraction equals space minus straight m squared straight y space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
rightwards double arrow space space space fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight m squared straight y space equals 0
                             

    Question 149
    CBSEENMA12032941

    Form the differential equation corresponding to y2 = m (a2 – x2) by eliminating m and a.

    Solution

    The given equation is straight y squared space equals space straight m left parenthesis straight a squared minus straight x squared right parenthesis                   ...(1)
    Differentiating w.r.t.x, we get,
    2 straight y dy over dx space equals space straight m left parenthesis 0 minus 2 space straight x right parenthesis
    or    straight y dy over dx space equals space minus straight m space straight x                                                ...(2)
    Again differentiating w.r.t.x,
                   straight y fraction numerator straight d squared straight y over denominator dx squared end fraction plus dy over dx. dy over dx space equals space minus straight m
    or             straight y space fraction numerator straight d squared straight y over denominator dx squared end fraction plus open parentheses dy over dx close parentheses squared space equals space minus open parentheses straight y fraction numerator begin display style dy over dx end style over denominator straight x end fraction close parentheses space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space space of space space left parenthesis 2 right parenthesis close square brackets
    or               xy fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight x open parentheses dy over dx close parentheses squared space equals space straight y dy over dx
    Which is the required differential equation.

    Question 150
    CBSEENMA12032942

    Form the differential equation corresponding to y2 = a (b – x) (b + x) by eliminating a and b.

    Solution
    The given equation is
                  straight y squared space equals straight a space left parenthesis straight b minus straight x right parenthesis space left parenthesis straight b plus straight x right parenthesis space space or space space straight y squared space equals straight a space left parenthesis straight b squared minus straight x squared right parenthesis                  ...(1)
    therefore space space space space space 2 straight y dy over dx space equals space straight a left parenthesis negative 2 straight x right parenthesis space or space straight y dy over dx space equals space minus ax                                 ...(2)
    Again straight y fraction numerator straight d squared straight y over denominator dx squared end fraction plus dy over dx. dy over dx space equals space minus straight a                                                 ...(3)
     Eliminating a from (2) and (3), we get,
                               straight y dy over dx space equals space xy fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight x open parentheses dy over dx close parentheses squared space space or space space straight x space straight y fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight x open parentheses dy over dx close parentheses squared minus straight y dy over dx equals 0
    which is the required differential equation.
    Question 151
    CBSEENMA12032943

    Form the differential equation of the family of curves represented by the equation (x – a)2 + 2 y2 = a2, a being the parameter.

    Solution
    The given equation is
                      open parentheses straight x minus straight a close parentheses squared plus 2 straight y squared space equals space straight a squared                    ...(1)
    Differentiating both sides w.r.t.x , we get.
                         2 left parenthesis straight x minus straight a right parenthesis plus 4 straight y dy over dx space equals 0 
    therefore space space                              straight x minus straight a equals negative 2 straight y dy over dx                 ...(2)
    and                             straight a equals straight x plus 2 straight y dy over dx                       ...(3)
    Putting the values of x - a, a from (2), (3) in (1), we get, 
                         open parentheses negative 2 straight y space dy over dx close parentheses squared plus 2 straight y squared space equals space open parentheses straight x plus 2 straight y dy over dx close parentheses squared
    or            4 straight y squared open parentheses dy over dx close parentheses squared plus 2 straight y squared space equals space straight x squared plus 4 straight y squared open parentheses dy over dx close parentheses squared plus 4 xy dy over dx
    or                                         2 straight y squared space equals space straight x squared plus 4 xy dy over dx
    or                               2 straight y squared minus straight x squared space equals space 4 xy dy over dx
    which is the required differential equation of the given family of curves. 
       
              
    Question 152
    CBSEENMA12032944

    Prove that x2 – y2 = c (x2 + y2 )2 is the general solution of differential equation (x3 – 3 x y2 ) dx = (y3 –3 x2 y) dy . where c is a parameter.

    Solution

    Here,                                 straight x squared minus straight y squared space equals space straight c left parenthesis straight x squared plus straight y squared right parenthesis squared                      ...(1)
    Differentiating w.r.t.x, we get,
                              2 straight x minus 2 straight y dy over dx space equals space 2 straight c left parenthesis straight x squared plus straight y squared right parenthesis. space open parentheses 2 straight x plus 2 straight y dy over dx close parentheses
                                       straight x minus straight y space dy over dx space equals space 2 straight c left parenthesis straight x squared plus straight y squared right parenthesis. space open parentheses straight x plus straight y dy over dx close parentheses          ...(2)
    Dividing (2) by (1), we get.
                           fraction numerator straight x minus straight y begin display style dy over dx end style over denominator straight x squared minus straight y squared end fraction space equals space fraction numerator 2 open parentheses straight x plus straight y begin display style dy over dx end style close parentheses over denominator straight x squared plus straight y squared end fraction
    therefore space space space straight x left parenthesis straight x squared plus straight y squared right parenthesis minus straight y left parenthesis straight x squared plus straight y squared right parenthesis space dy over dx space equals space 2 straight x left parenthesis straight x squared minus straight y squared right parenthesis plus 2 straight y left parenthesis straight x squared minus straight y squared right parenthesis dy over dx
therefore space space space space space open square brackets 2 space straight y space left parenthesis straight x squared minus straight y squared right parenthesis space plus space straight y left parenthesis straight x squared plus straight y squared right parenthesis close square brackets dy over dx space equals space straight x left parenthesis straight x squared plus straight y squared right parenthesis minus 2 straight x left parenthesis straight x squared minus straight y squared right parenthesis
therefore space space space left parenthesis 2 straight x squared straight y minus 2 straight y cubed plus straight x squared straight y plus straight y cubed right parenthesis dy over dx space equals space straight x cubed plus xy squared minus 2 straight x cubed plus 2 xy squared
therefore space space space space left parenthesis 3 straight x squared straight y minus straight y cubed right parenthesis dy over dx space equals space 3 xy squared minus straight x cubed
therefore space space space space space space space space space space space space space space space space space space space space space space space space space space space dy over dx space equals space fraction numerator straight x cubed minus 3 xy squared over denominator straight y cubed minus 3 straight x squared straight y end fraction space which space is space the space required space equation.
    Hence the result. 

    Question 153
    CBSEENMA12032946

    Form a differential equation from the equation y = 2(x2 - 1) + ce-x2.

    Solution

    The given equation is
    y = 2 (x2 - 1) + c e-x2 or yex2 = 2 (x21) ex2 + c
    Differentiating both sides w.r.t. x, we get.
                         straight y. straight e to the power of straight x squared end exponent. space 2 space straight x space plus space straight e to the power of straight x squared end exponent. space dy over dx space equals space 2 left parenthesis straight x squared minus 1 right parenthesis space straight e to the power of straight x squared end exponent. space 2 space straight x space plus space 2 straight e to the power of straight x squared end exponent. space space 2 straight x space plus space 0
    or          2 xy plus dy over dx space equals space 4 straight x left parenthesis straight x squared minus 1 right parenthesis space plus space 4 straight x space space space space space or space space space dy over dx space equals space 4 straight x left parenthesis straight x squared minus 1 right parenthesis space plus space 4 straight x space minus space 2 xy
    which is required differential equation. 

    Question 154
    CBSEENMA12032947

    Form the differential equation of the family of curves
    straight y equals Ax plus straight B over straight x
    where A and B are constants.

    Solution

    The given equation is
                          straight y equals Ax plus straight B over straight x                                     ...(1)
    therefore space space space dy over dx space equals space straight A minus straight B over straight x squared                                              ...(2)
    rightwards double arrow space space fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space fraction numerator 2 straight B over denominator straight x cubed end fraction                                                  ...(3)
    From (3), B = straight x cubed over 2 fraction numerator straight d squared straight y over denominator dx squared end fraction
    From  (2),  dy over dx space equals space straight A minus straight x over 2 fraction numerator straight d squared straight y over denominator dx squared end fraction space space rightwards double arrow space space space straight A space equals space straight x over 2 fraction numerator straight d squared straight y over denominator dx squared end fraction plus dy over dx
    Putting value of A and B in (1), we get,
                                    straight y space equals straight x squared over 2 fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight x dy over dx plus straight x squared over 2 fraction numerator straight d squared straight y over denominator dx squared end fraction space space space or space space space straight x squared fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight x dy over dx minus straight y space equals 0
    which is the required differential equation. 

    Question 155
    CBSEENMA12032949

    Form the differential equation of the family of curves
    straight y equals Ae to the power of Bx
    where A and B are constants.

    Solution
    The given equation is
                             straight y space equals space straight A space straight e to the power of Bx                                        ...(1)
    therefore space space space space dy over dx space equals space straight A space straight B space straight e to the power of Bx space space space space space space space space or space space space space space dy over dx space equals space straight B space straight y              ...(2)
                                                                           open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
    therefore space space space fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space straight B dy over dx                                                   ...(3)
    From (2) and (3),  dy over dx space equals space fraction numerator straight y begin display style fraction numerator straight d squared straight y over denominator dx squared end fraction end style over denominator begin display style dy over dx end style end fraction
    or              straight y fraction numerator straight d squared straight y over denominator dx squared end fraction space equals open parentheses dy over dx close parentheses squared which is the required differential equation. 
    Question 156
    CBSEENMA12032951

    Form the differential equation of the family of curves
    straight y equals Ae to the power of straight x plus Be to the power of negative straight x end exponent
    where A and B are constants.

    Solution

    The given equation is
                               straight y equals Ae to the power of straight x plus Be to the power of negative straight x end exponent                          ...(1)
    therefore space space space dy over dx space equals space Ae to the power of straight x minus Be to the power of negative straight x end exponent space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space rightwards double arrow space space space space fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space Ae to the power of straight x plus Be to the power of negative straight x end exponent
    rightwards double arrow space space space space fraction numerator straight d squared straight y over denominator dx squared end fraction equals space straight y                                                       open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
    which is required differential equation. 

    Question 157
    CBSEENMA12032952

    Form the differential equation of the family of curves by eliminating arbitrary constants a and b.
    y = a e3x + be-2x

    Solution
    The equation of family of curves is
    y = a e3x + be-2x                       ...(1)
    Differentiating both sides w.r.t.x, we get
                     straight y subscript 1 space equals 3 space straight a space straight e to the power of 3 straight x end exponent space minus space 2 space straight b space straight e to the power of negative 2 straight x end exponent                ...(2)
    Again differentiating w.r.t. x, we get, 
                     straight y subscript 2 space equals space 9 space straight a space straight e to the power of 3 straight x end exponent plus 4 space be to the power of negative 2 straight x end exponent                  ...(3)
    Mutliplying (2) by 3 subtracting from (3), we get, 
                          straight y subscript 2 minus 3 straight y subscript 1 space equals space 10 space straight b space straight e to the power of negative 2 straight x end exponent
    therefore space space space space straight b space straight e to the power of negative 2 straight x end exponent space equals space 1 over 10 left parenthesis straight y subscript 2 minus 3 straight y subscript 1 right parenthesis                            ...(4)
    Multiplying (2) by 2 and adding it to (3), we get,
                    straight y subscript 2 plus 2 straight y subscript 1 space equals space 15 space straight a space straight e to the power of 3 straight x end exponent
    therefore space space space space space space space space ae to the power of 3 straight x end exponent space equals space 1 over 15 left parenthesis straight y subscript 2 plus 2 straight y subscript 1 right parenthesis                            ...(5)
    From (1), (4) and (5), we get,
                                   straight y space equals space 1 over 15 left parenthesis straight y subscript 2 plus 2 straight y subscript 1 right parenthesis+1 over 10 left parenthesis straight y subscript 2 minus 3 straight y subscript 1 right parenthesis
    or                         straight y equals 1 over 15 straight y subscript 2 plus 2 over 15 straight y subscript 1 plus 1 over 10 straight y subscript 2 minus 3 over 10 straight y subscript 1
    or                 open parentheses 1 over 15 plus 1 over 10 close parentheses space straight y subscript 2 space plus space open parentheses 2 over 15 minus 3 over 10 close parentheses space straight y subscript 1 minus straight y space equals space 0
    or          open parentheses fraction numerator 2 plus 3 over denominator 30 end fraction close parentheses space straight y subscript 2 plus space open parentheses fraction numerator 4 minus 9 over denominator 30 end fraction close parentheses space straight y subscript 1 space minus space straight y space equals space 0
    or      1 over 6 straight y subscript 2 minus 1 over 6 straight y subscript 1 minus straight y space equals space 0
    or            straight y subscript 2 minus straight y subscript 1 minus 6 straight y equals 0 comma space which is required differential equation.n
    Question 158
    CBSEENMA12032955

    Form the differential equation of the family of curves by eliminating arbitrary constants a and b.
    y = e2x (a + b x)

    Solution

    The equation of family of curves is
    y = e2x (a + b x)    ...(1)
    Differentiating both sides w.r.t. x, we get,
    y1 = e2x  b + (a + b x). 2 e2x
    or    y1 = b e2x + 2 y    [∵ of(1)]
    ∴ y1 – 2 y = be2x        ...(2)
    Again differentiating w.r.t. x, we get,
    y2 – 2 y1 = 2 b e2x
    or    y2 – 2 y1 = 2 (y1 – 2 y)    [∵ of (2)]
    or    y2 – 2 y1 = 2 y1 – 4 y
    or    y2 – 4 y1 + 4 y = 0, which is required differential equation.

    Question 159
    CBSEENMA12032956

    Form the differential equation of the family of curves by eliminating arbitrary constants a and b.
    y = ex (a cosx + b sinx)

    Solution
    The given equation is
           y = ex (a cosx + b sinx)                             ...(1)
    Differentiating both sides w.r.t x, we get
                        dy over dx equals straight e to the power of straight x left parenthesis straight a space cosx plus space straight b space sinx right parenthesis space plus straight e to the power of straight x left parenthesis negative straight a space sinx space plus space straight b space cosx right parenthesis
    or            dy over dx equals straight y plus straight e to the power of straight x left parenthesis negative straight a space sin space straight x space plus space straight b space cosx right parenthesis     ...(2)
                                                                                   open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
    Again differentiating w.r.t x,
                  fraction numerator straight d squared straight y over denominator dx squared end fraction equals space dy over dx plus straight e to the power of straight x left parenthesis negative straight a space sinx space plus space straight b space cosx right parenthesis space plus space straight e to the power of straight x left parenthesis negative straight a space cosx space minus space straight b space sinx right parenthesis
    or        fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space dy over dx plus open parentheses dy over dx minus straight y close parentheses space minus space straight e to the power of straight x left parenthesis straight a space cosx space plus space straight b space sinx right parenthesis space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 2 right parenthesis close square brackets
    or        fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space dy over dx plus dy over dx minus straight y minus straight y                                                 open square brackets because space space of space space left parenthesis 1 right parenthesis close square brackets
    or         fraction numerator straight d squared straight y over denominator dx squared end fraction minus 2 dy over dx plus 2 straight y equals 0, which is required differential equation. 
    Question 160
    CBSEENMA12032958

    Form a differential equation from the equation y = ae 2x + be– 3x , a , b being constants. 

    Solution

    The given equation is
                            y = ae 2x + be– 3x                            ...(1)
    Differentiating both sides w.r.t.x, we get
                            dy over dx space equals space 2 ae to the power of 2 straight x end exponent minus 3 be to the power of negative 3 straight x end exponent               ...(2)
    Again differentiation both sides w.r.t.x, we get.
              fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space 4 ae to the power of 2 straight x end exponent plus 9 be to the power of negative 3 straight x end exponent                            ...(3)
    Multiplying (2) by 2 and subtracting from (3), we get,
                fraction numerator straight d squared straight y over denominator dx squared end fraction minus 2 dy over dx space equals space 15 space be to the power of negative 3 straight x end exponent
    therefore space space space space space be to the power of negative 3 straight x end exponent space equals 1 over 15 open parentheses fraction numerator straight d squared straight y over denominator dx squared end fraction minus 2 dy over dx close parentheses                     ...(4)
    Multiplying (2) by 3 and adding it to (3), we get,
                            fraction numerator straight d squared straight y over denominator dx squared end fraction plus 3 dy over dx space equals space 10 space straight a space straight e to the power of 2 straight x end exponent
    therefore space space space space space space ae to the power of 2 straight x end exponent space equals space 1 over 10 open parentheses fraction numerator straight d squared straight y over denominator dx squared end fraction plus 3 dy over dx close parentheses                       ...(5)
    From (1), (4) and (5), we get,
                                 straight y equals space 1 over 10 open parentheses fraction numerator straight d squared straight y over denominator dx squared end fraction plus 3 dy over dx close parentheses plus 1 over 15 open parentheses fraction numerator straight d squared straight y over denominator dx squared end fraction minus 2 dy over dx close parentheses
    or                       30 space straight y space equals space 3 space fraction numerator straight d squared straight y over denominator dx squared end fraction plus 9 dy over dx plus 2 fraction numerator straight d squared straight y over denominator dx squared end fraction minus 4 dy over dx
    or             5 fraction numerator straight d squared straight y over denominator dx squared end fraction plus 5 dy over dx space equals space 30 space straight y space space space space space or space space space fraction numerator straight d squared straight y over denominator dx squared end fraction plus dy over dx minus 6 straight y space equals space 0
    which is required differential equation. 
     

    Question 161
    CBSEENMA12032959

    Form the differential equation of the following family of curves:
    x y = A ex + B e–x + x2 

    Solution
    The equation of the family of curves is
    x y = A ex + B e–x + x2                                ...(1)
    Differentiating both sides w.r.t. x, we get,
                 straight x dy over dx plus straight y space.1 space equals space Ae to the power of straight x minus Be to the power of negative straight x end exponent plus 2 straight x
    Again differentiating both sides w.r.t. x, we get,
                 straight x fraction numerator straight d squared straight y over denominator dx squared end fraction plus dy over dx.1 plus dy over dx space equals space straight A space straight e to the power of straight x plus Be to the power of negative straight x end exponent plus 2
    or      straight x fraction numerator straight d squared straight y over denominator dx squared end fraction plus 2 dy over dx space equals space xy space minus straight x squared plus 2                       open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
    which is required differential equation.
    Question 162
    CBSEENMA12032961

    Find the differential equation of the family of curves y = aex + be2x + ce3x, where a, b. c are arbitrary constants.

    Solution

    The given equation is
    y = aex + be2x + ce3x    ...(1)
    ∴ y1 = (aex + 2be2x – 3ce – 3x)   ...(2)
    Subtracting (1) from (2), we get,
    y1 – y = b e2x – 4 c e–3x    ...(3)
    ∴    y2 – y1 = 2 b e2x + 12 c e–3x    ...(4)
    Multiplying (3) by 2 and subtracting from (3), are get,
    y2 – 3 y1 + 2 y = 20 c e–3x    ...(5)
    ∴  y3 – 3 y2 + 2 y1 = – 60 c e –3x    ...(6)
    Multiplying (5) by 3 and adding to (6), we get ,
    (y3 – 3 y2 + 2 y1) + 3 (y2 – 3 y1 + 2 y) = 0 or y3 – 7 y1 + 6 y = 0
    which is required differential equation.

    Question 163
    CBSEENMA12032962

    Obtain the differential equation from  the equation y = ex (a cos 2x + b sin 2x). where a and b are arbitrary constants.    

    Solution

    The given equation is
                          y = ex (a cos 2x + b sin 2x)     ... (1)
    Differentiating both sides w.r.t x, we get,
                         dy over dx space equals space straight e to the power of straight x left parenthesis straight a space cos space 2 straight x space plus space straight b space sin space 2 straight x right parenthesis space plus space straight e to the power of straight x left parenthesis negative 2 straight a space sin space 2 straight x space plus space 2 straight b space cos space 2 straight x right parenthesis    
    therefore space space space space dy over dx space equals space straight y plus straight e to the power of straight x left parenthesis negative 2 straight a space sin space 2 straight x space plus space 2 straight b space cos space 2 straight x right parenthesis    ...(2)
                                                                                      open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
    Again differentiating w.r.t x,
           space space space space space space space fraction numerator straight d squared straight y over denominator dx squared end fraction space equals dy over dx plus straight e to the power of straight x left parenthesis negative 2 straight a space sin space 2 straight x space plus space 2 straight b space cos space 2 straight x right parenthesis space plus space straight e to the power of straight x left parenthesis negative 4 straight a space cos space 2 straight x space minus space 4 straight b space sin space 2 straight x right parenthesis
    or          fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space dy over dx plus open parentheses dy over dx minus straight y close parentheses minus 4 straight e to the power of straight x left parenthesis straight a space cos space 2 straight x space plus space straight b space sin space 2 straight x right parenthesis space space space space space space open square brackets because space of space left parenthesis 2 right parenthesis close square brackets
    or          fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space dy over dx plus dy over dx minus straight y minus 4 straight y space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
    or          fraction numerator straight d squared straight y over denominator dx squared end fraction minus 2 dy over dx plus 5 straight y space equals space 0
    which is required differential equation. 

    Question 164
    CBSEENMA12032964

    Find the differential equation of the family of curves y = a sin (bx + c). a, b. c being arbitrary constants.

    Solution
    The given equation is
                           y = a sin (bx + c)                             ...(1)
    Differentiating w.r.t.x, successively three times,
                         dy over dx space equals straight b space straight a space cos left parenthesis bx plus straight c right parenthesis                     ...(2)
                fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space minus straight b squared straight a space sin left parenthesis bx plus straight c right parenthesis                       ...(3)
             fraction numerator straight d cubed straight y over denominator dx cubed end fraction space equals space minus straight b cubed straight a space cos left parenthesis bx plus straight c right parenthesis                         ...(4)
    From (1) and (2), (3) and (4), we get,
                 straight y fraction numerator straight d cubed straight y over denominator dx cubed end fraction equals negative straight b cubed straight a squared space sin space left parenthesis bx plus straight c right parenthesis space cos space left parenthesis bx plus straight c right parenthesis
                                equals space left square bracket straight b space straight a space cos space left parenthesis bx plus straight c right parenthesis right square bracket space left square bracket straight b squared straight a space sin left parenthesis bx plus straight c right parenthesis right square bracket
    or           straight y fraction numerator straight d cubed straight y over denominator dx cubed end fraction space equals space open parentheses dy over dx close parentheses space fraction numerator straight d squared straight y over denominator dx squared end fraction is the required differential equation. 
    Question 165
    CBSEENMA12032965

    Form the differential equation of the family of circles having centre on x-axis and passing through the origin.    

    Solution

    Let the radius of circle = a
    Since the circle has centre on x-axis and passes through the origin.
    ∴ its centre is (a, 0)
    The equation of circle is
    ( x – a)2+( y – 0)2 = a or x2 –2 a x + a2 + y2 = a2
    ∴       x+ y2 – 2 ax = 0    ...(1)
    Differentiating both sides w.r.t. x, we get.
                               2 straight x plus 2 straight y dy over dx minus 2 straight a space equals space 0 space space space space space space space space space space space space or space space space space space space straight x plus straight y dy over dx minus straight a space equals space 0
    therefore space space space space space space space space space space space straight a space equals space straight x plus straight y dy over dx
    Putting this value of a in (1), we get.
                                 straight x squared plus straight y squared minus 2 straight x open parentheses straight x plus straight y dy over dx close parentheses space equals space 0
    therefore space space space straight x squared plus straight y squared minus 2 straight x squared minus 2 xy dy over dx space equals space 0
therefore space space space space minus straight x squared plus straight y squared minus 2 xy dy over dx space equals space 0
therefore space space space space space space 2 space xy dy over dx plus straight x squared minus straight y squared space equals space 0
    which is required differential equation. 

    Question 166
    CBSEENMA12032967

    Determine the differential equation that will represent the family of all circles having centres on the x-axis and radius unity.

    Solution
    Let centre on x-axis be (a. 0). Also radius = 1
    ∴    the equation of the family of circles is
                 open parentheses straight x minus straight a close parentheses squared plus left parenthesis straight y minus 0 right parenthesis squared space equals space 1 space space space space space space space space space space space space or space space space space space space left parenthesis straight x minus straight a right parenthesis squared plus straight y squared space equals 1 space                 ...(1)
    Differentiating w.r.t x, we get,
                 2 left parenthesis straight x minus straight a right parenthesis plus 2 straight y dy over dx space equals 0             or      straight x minus straight a space equals space minus straight y dy over dx
    Putting this value of x - a in (1), we get,
                                    open parentheses negative straight y dy over dx close parentheses squared plus straight y squared space equals space 1 space space space space space space space space space space space space space space space space space space space space or space space space space space space space straight y squared open parentheses dy over dx close parentheses squared plus straight y squared space equals space 1
    which is required differential equation. 
    Question 167
    CBSEENMA12032969

    Form the differential equation of the family of circles having centre on x-axis and radius 3 units.

    Solution

    The equation of the family of circles having centre (0, b) on y-axis and radius 3 units is
    x2 + (y – b)2 = 9    ...( 1)
    Differentiating both sides w.r.t x, we get,
                   2 straight x plus 2 left parenthesis straight y minus straight b right parenthesis dy over dx space equals space 0 space space space or space space space straight y space minus space straight b space equals space minus fraction numerator straight x over denominator begin display style dy over dx end style end fraction
    Putting this value of y - b in (1), we get,
                            straight x squared plus straight x squared over open parentheses begin display style dy over dx end style close parentheses squared space equals space 9    or     open parentheses straight x squared minus 9 close parentheses plus straight x squared over open parentheses begin display style dy over dx end style close parentheses squared space equals 0
    or                   left parenthesis straight x squared minus 9 right parenthesis space open parentheses dy over dx close parentheses squared plus straight x squared space equals space 0
    which is required differential equation.

    Question 168
    CBSEENMA12032972

    Find the differential equation of all the circles in the first quadrant which touch the co-ordinate axes.

    Solution

    Let r be the radius of the circle whose centre is C and CM ⊥ x-axis, CN ⊥ y-axis.
    ∵  circle touches both the axes
    ∴     CM = CN = r
    ∴   C is (r, r)
    ∴  equation of circle is
    (x - r)2 + (y – r)2 = r2    ...(1)
    Differentiating both sides w.r.t.x,
                               2 left parenthesis straight x minus straight r right parenthesis plus 2 left parenthesis straight y minus straight r right parenthesis space dy over dx space equals space 0
    or                      open parentheses straight x minus straight r close parentheses plus left parenthesis straight y minus straight r right parenthesis space straight y subscript 1 space equals space 0
    or                                    straight x plus straight y space straight y subscript 1 space equals space left parenthesis 1 plus straight y subscript 1 right parenthesis straight r space space space rightwards double arrow space space space space straight r space equals space fraction numerator straight x plus space straight y space straight y subscript 1 over denominator 1 plus straight y subscript 1 end fraction
    Putting this value of r in (1), we get
                                        open parentheses straight x minus fraction numerator straight x plus space straight y space straight y subscript 1 over denominator 1 plus space straight y subscript 1 end fraction close parentheses squared plus space open parentheses straight y minus fraction numerator straight x space plus straight y space straight y subscript 1 over denominator 1 plus straight y subscript 1 end fraction close parentheses squared space equals space open parentheses fraction numerator straight x plus straight y space straight y subscript 1 over denominator 1 plus space straight y subscript 1 end fraction close parentheses squared
    or         left parenthesis straight x plus space straight x space straight y subscript 1 space minus straight x minus space straight y space straight y subscript 1 right parenthesis squared plus space left parenthesis straight y space plus space straight y space straight y subscript 1 minus straight x minus space straight y space straight y subscript 1 right parenthesis squared space equals space left parenthesis straight x space plus space straight y space straight y subscript 1 right parenthesis squared
    or                                                    open square brackets left parenthesis straight x minus straight y right parenthesis space straight y subscript 1 close square brackets squared plus left parenthesis straight y minus straight x right parenthesis squared space equals space left parenthesis straight x plus straight y space straight y subscript 1 right parenthesis squared
    or                                                             open parentheses straight x minus straight y close parentheses squared plus left parenthesis 1 plus straight y subscript 1 squared right parenthesis space equals space left parenthesis straight x plus straight y space straight y subscript 1 right parenthesis squared
    which is the required differential equation. 

    Question 169
    CBSEENMA12032974

    Form the differential equation of the family of circles in the second quadrant and touching the coordinate axes.

    Solution
    Let C denote the family of circles in the second quadrant and touching the coordinate axes. Let (– a, a) be the coordinate of the centre of any member of this family.

    Equation representing the family C is
    (x + a)2+ (y – a)2 = a2    ...(1)
    or x2 + y2 + 2 ax – 2 a y + a2 = 0    ...(2)
    Differentiating equation (2) with respect to x, we get
                               2 straight x plus 2 straight y dy over dx plus 2 straight a minus 2 straight a dy over dx equals 0
    or              straight x plus straight y dy over dx space equals straight a open parentheses dy over dx minus 1 close parentheses
    or                             straight a equals fraction numerator straight x plus straight y space straight y apostrophe over denominator straight y apostrophe minus 1 end fraction
    Substituting the value of a in equation (1), we get
                                      open square brackets straight x plus fraction numerator straight x plus straight y space straight y apostrophe over denominator straight y apostrophe minus 1 end fraction close square brackets squared plus open square brackets straight y minus fraction numerator straight x plus straight y space straight y apostrophe over denominator straight y apostrophe minus 1 end fraction close square brackets squared space equals space open square brackets fraction numerator straight x plus straight y space straight y apostrophe over denominator straight y apostrophe minus 1 end fraction close square brackets squared
    or        open square brackets xy apostrophe space minus straight x plus straight x plus straight y space straight y apostrophe close square brackets squared plus open square brackets straight y space straight y apostrophe space minus straight y space minus space straight x space minus space straight y space straight y apostrophe close square brackets squared space equals open square brackets straight x plus straight y space straight y apostrophe close square brackets squared
    or         left parenthesis straight x plus straight y right parenthesis squared space straight y apostrophe squared space plus space open square brackets straight x plus straight y close square brackets squared space equals space open square brackets straight x plus space straight y space straight y apostrophe close square brackets squared
    or        left parenthesis straight x plus straight y right parenthesis squared space left square bracket left parenthesis 1 plus left parenthesis straight y apostrophe right parenthesis squared right square bracket space equals space left square bracket straight x plus straight y space straight y apostrophe right square bracket squared
    which is the differential equation representing the given family of circles.

    Question 170
    CBSEENMA12032975

    Form the differential equation of the family of circles touching the x-axis at origin.

    Solution

    Let C denote the family of circles touching x-axis at origin. Let (0, a) be the coordinates of the centre of any member of the family where ‘a’ is an arbitrary constant.
    ∴    the equation of family C is
    x2 + (y – a)2 = a2
    ∴   x2 + y2 + a2 – 2 a y = a2
    or x2 + y2 – 2 a y = 0    ...(1)
    a being arbitrary constant

    Differentiating w.r.t. x, we get
               2 straight x plus 2 straight y dy over dx minus 2 straight a dy over dx space equals space 0
    therefore              2 xy plus 2 straight y squared dy over dx minus 2 ay dy over dx space equals space 0                       ...(2)
                                                                                        [Multiplying by y]
    Multiplying (1) by dy over dx comma space we space get comma
                          left parenthesis straight x squared plus straight y squared right parenthesis space dy over dx space minus space 2 ay dy over dx space equals space 0                  ...(3)
    Subtracting (3) from (2), we get, 
                         2 xy plus 2 straight y squared dy over dx minus left parenthesis straight x squared plus straight y squared right parenthesis dy over dx space equals space 0 space space or space space 2 xy plus left parenthesis straight y squared minus straight x squared right parenthesis space dy over dx equals 0
    or             open parentheses straight x squared minus straight y squared close parentheses space dy over dx space equals space 2 xy     or   dy over dx space equals space fraction numerator 2 xy over denominator straight x squared minus straight y squared end fraction
    which is required differential equation.

    Question 171
    CBSEENMA12032976

    Form the differential equation of the family of circles touching the y-axis at origin.

    Solution

    The equation of family of circles touching y-axis at origin is
    (x – h)2 + y2 = h2 where h is arbitrary constant    ...(1)
    [∵ if (h, 0) is centre of any member of family, then its radius = h]
    Differentiating (1) w.r.t.x,  2 left parenthesis straight x minus straight h right parenthesis plus 2 straight y dy over dx space equals space 0
    ⇒ x – h + y y1= 0 ⇒ h = x + y y1
    Putting value of h in (1), we get,
    (x – x – y y1)2 + y2 = (x + y y1)2 ⇒ y2 y12 + y2 = y2 + 2 x y y1 + y2 y12
    ⇒ x2 – y2 + 2 x y y1 = 0 , which is the required differential equation.

    Question 172
    CBSEENMA12032978

    Form the differential equation of the family of parabolas having vertex at origin and axis along positive direction of x-axis.

    Solution

    Let P denote the family of given parabolas and let (a, 0) be the 'focus of a member of the given family, where a is an arbitrary constant. Therefore, equation of family P is
    y2 = 4 a x    ...(1)
    Differentiating both sides with respect to x, we get
    2 straight y dy over dx space equals space 4 straight a       ...(2)

    Substituting the value of 4 a from equation (2) in equation (1), we get
    straight y squared space equals space open parentheses 2 straight y space dy over dx close parentheses space left parenthesis straight x right parenthesis space space space space or space space space straight y squared minus 2 xy dy over dx space equals space 0
    which is the differential equation of the given family of parabolas.

    Question 173
    CBSEENMA12032979

    Form the differential equation of the family of parabolas having vertex at origin and axis along positive direction of y-axis.

    Solution

    Let P denote the family of parabolas and let S (0. a) be the focus of a member of the given family, where a is an arbitrary constant.
    ∴    equation of family P is
    a2 = 4 a y    ...(1)
    Differentiating both sides w.r.t. x, we get.
                               2 straight x space equals space 4 straight a dy over dx
    therefore space space space space 4 straight a space equals space fraction numerator 2 straight x over denominator begin display style dy over dx end style end fraction
    Putting value of 4a in (1), we get,
                                straight x squared space equals space fraction numerator 2 straight x over denominator begin display style dy over dx end style end fraction straight y space space space or space space space space straight x dy over dx space equals space 2 straight y
    which is the required differential equation. 


    Question 174
    CBSEENMA12032982

    Form the differential equation representing the family of ellipses having foci on x-axis and centre at the origin.

    Solution
    The general equation of such ellipse is
    straight x squared over straight a squared plus straight y squared over straight b squared space equals space 1 space space left parenthesis straight a comma space space straight b space being space arbitrary space constants right parenthesis     ...(1)

    Differentiating w.r.t. x successively two times, we get.
                   fraction numerator 2 straight x over denominator straight a squared end fraction plus fraction numerator 2 straight y space straight y subscript 1 over denominator straight b squared end fraction space equals space 0 space space space space or space space straight x over straight a squared plus fraction numerator straight y space straight y subscript 1 over denominator straight b squared end fraction space equals space 0              ...(2)
    rightwards double arrow space space space space straight a squared over straight b squared space equals space minus fraction numerator straight x over denominator straight y space straight y subscript 1 end fraction                                                               ...(3)
    and 1 over straight a squared plus fraction numerator straight y space straight y subscript 2 plus space straight y subscript 1 squared over denominator straight b squared end fraction space equals space 0 space space space space space space space space rightwards double arrow space space space space straight a squared over straight b squared space equals space fraction numerator negative 1 over denominator straight y space straight y subscript 2 space plus space straight y subscript 1 squared end fraction             ...(4)
    From (3), (4), we get
                         fraction numerator negative straight x over denominator straight y space straight y subscript 1 end fraction space equals space fraction numerator negative 1 over denominator straight y space straight y subscript 2 space plus space straight y subscript 1 squared end fraction space space space space space space rightwards double arrow space space space space space straight x left parenthesis straight y space straight y subscript 2 plus straight y subscript 1 squared right parenthesis space minus space straight y space straight y subscript 1 space equals space 0
    which is the required differential equation.
    Question 175
    CBSEENMA12032984

    Form the differential equation of the family of ellipses having foci on y-axis and centre at origin.

    Solution
    The equation of family of ellipses having foci on y-axis and centre at origin is
                        straight x squared over straight a squared plus straight y squared over straight a squared space equals space 1                            ...(1)
     Differentiating w.r.t. x, we get,
                                fraction numerator 2 straight x over denominator straight b squared end fraction plus fraction numerator 2 straight y over denominator straight a squared end fraction dy over dx space equals space 0              ...(2)
    therefore space space space space space space space straight a squared over straight b squared space equals space fraction numerator negative straight y over denominator straight x end fraction dy over dx                                                              ...(3)
    Again differentiating (2) w.r.t.x, we get,
                             2 over straight b squared plus fraction numerator 2 straight y over denominator straight a squared end fraction fraction numerator straight d squared straight y over denominator dx squared end fraction plus 2 over straight a squared open parentheses dy over dx close parentheses squared space space equals space 0
    therefore space space space space space space space space space space space space space space space space space space space space space space space space space space space straight a squared over straight b squared space equals space minus open square brackets straight y fraction numerator straight d squared straight y over denominator dx squared end fraction plus open parentheses dy over dx close parentheses squared close square brackets                       ...(4)
    From (3) and (4), we get,
       space space space space space space space space space space space space space space space space space space space space space space space space minus straight y over straight x dy over dx space equals space minus open square brackets straight y fraction numerator straight d squared straight y over denominator dx squared end fraction plus open parentheses dy over dx close parentheses squared close square brackets
therefore space space space space space space space space space space space space space space space space space space space space straight y over straight x dy over dx equals space straight x space straight y space fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight x open parentheses dy over dx close parentheses squared
    which is required differential equation.
    Question 176
    CBSEENMA12032985

    Form the differential equation of the family of hyperbolas having foci on x-axis and centre at origin.

    Solution
    The equation of family of hyperbolas having foci on x-axis and centre at origin is
                  straight x squared over straight a squared minus straight y squared over straight b squared space equals 1                             ...(1)
    Differentiating w.r.t.. x successively two times, we get,
                               fraction numerator 2 straight x over denominator straight a squared end fraction minus fraction numerator 2 space straight y space straight y subscript 1 over denominator straight b squared end fraction space equals space 0 space space space space space space space space space space space space space space space space space space rightwards double arrow space space space space space straight x over straight a squared minus fraction numerator straight y space straight y subscript 1 over denominator straight b squared end fraction space equals space 0
    rightwards double arrow space space space space space space space space space space space space space space space space space space space space space space space space space straight a squared over straight b squared space equals fraction numerator straight x over denominator straight y space straight y subscript 1 end fraction                ...(2)
    and     1 over straight a squared minus fraction numerator straight y space straight y subscript 2 plus straight y subscript 1 squared over denominator straight b squared end fraction space equals space 0 space space space space space space space space space space space space space space space rightwards double arrow space space space space straight a squared over straight b squared space equals space fraction numerator 1 over denominator straight y space straight y subscript 2 space plus space straight y subscript 1 squared end fraction              ...(3)
    From (2), (3), we get,
                             fraction numerator straight x over denominator straight y space straight y subscript 1 end fraction space equals space fraction numerator 1 over denominator straight y space straight y subscript 2 plus straight y subscript 1 squared end fraction space space or space space straight x thin space left parenthesis straight y space straight y subscript 2 plus straight y subscript 1 squared right parenthesis space minus space straight y space straight y subscript 1 space equals space 0
    which is the required differential equation. 
    Question 177
    CBSEENMA12032986

    Which of the following differential equations has y = c1ex + c2e–x as the general solution?
    • fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight y space equals space 0
    • fraction numerator straight d squared straight y over denominator dx squared end fraction minus straight y space equals space 0
    • fraction numerator straight d squared straight y over denominator dx squared end fraction plus 1 space equals space 0
    • fraction numerator straight d squared straight y over denominator dx squared end fraction minus 1 space equals space 0

    Solution

    B.

    fraction numerator straight d squared straight y over denominator dx squared end fraction minus straight y space equals space 0

    The given equation is
                            straight y space equals straight c subscript 1 straight e to the power of straight x plus straight c subscript 2 straight e to the power of negative straight x end exponent                                ...(1)
    therefore space space space space space dy over dx space equals space straight c subscript 1 straight e to the power of straight x minus straight c subscript 2 straight e to the power of negative straight x end exponent
rightwards double arrow space space space space fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space straight c subscript 1 straight e to the power of straight x plus straight c subscript 2 straight e to the power of negative straight x end exponent space space space rightwards double arrow space space space fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space straight y space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
rightwards double arrow space space space space space space fraction numerator straight d squared straight y over denominator dx squared end fraction minus straight y space equals space 0 comma space space which space is space the space required space differential space equation.
    therefore   (B) is the correct answer.

     
    Question 178
    CBSEENMA12032988

    Which of the following differential equations has y = x as one of its particular solution?
    • fraction numerator straight d squared straight y over denominator dx squared end fraction minus straight x squared dy over dx plus straight x space straight y space equals straight x
    • fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight x dy over dx plus straight x space straight y space equals space straight x
    • fraction numerator straight d squared straight y over denominator dx squared end fraction minus straight x squared dy over dx plus straight x space straight y space equals space 0
    • fraction numerator straight d squared straight y over denominator dx squared end fraction plus straight x dy over dx plus xy space equals space 0

    Solution

    C.

    fraction numerator straight d squared straight y over denominator dx squared end fraction minus straight x squared dy over dx plus straight x space straight y space equals space 0

    Here y = x
    therefore space space space space space space space space space space space space space space space space space space space space dy over dx space equals space 1 comma space space space space fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space 0
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#2 [internal function]: _hx_lambda->execute('Http Error #502')
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(532): call_user_func_array(Array, Array)
#4 [internal function]: haxe_Http_5(true, Object(com_wiris_plugin_impl_HttpImpl), Object(com_wiris_plugin_impl_HttpImpl), Array, Object(haxe_io_BytesOutput), true, 'Http Error #502')
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#6 [internal function]: _hx_lambda->execute('Http Error #502')
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#8 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(444): com_wiris_plugin_impl_HttpImpl->onError('Http Error #502')
#9 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(458): haxe_Http->customRequest(true, Object(haxe_io_BytesOutput), NULL, NULL)
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#13 {main}</pre>
    <pre>uncaught exception: <b>Http Error #404</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php line 61<br />#0 [internal function]: com_wiris_plugin_impl_HttpImpl_0(Object(com_wiris_plugin_impl_HttpImpl), NULL, 'http://www.wiri...', 'Http Error #404')
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#2 [internal function]: _hx_lambda->execute('Http Error #404')
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#4 [internal function]: haxe_Http_5(true, Object(com_wiris_plugin_impl_HttpImpl), Object(com_wiris_plugin_impl_HttpImpl), Array, Object(haxe_io_BytesOutput), true, 'Http Error #404')
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#6 [internal function]: _hx_lambda->execute('Http Error #404')
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#8 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(444): com_wiris_plugin_impl_HttpImpl->onError('Http Error #404')
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#13 {main}</pre>                         open square brackets because space space 0 minus straight x squared space cross times space 1 space plus straight x. space straight x space equals space 0 space or space space 0 space equals space 0 close square brackets
    therefore space space space left parenthesis straight C right parenthesis space is space correct space answer.

    Question 179
    CBSEENMA12032990

    Solve straight y apostrophe minus dy over dx space equals space minus straight x over straight y space left parenthesis straight y not equal to 0 right parenthesis.

    Solution
    The given differential equation is
    dy over dx equals negative straight x over straight y
    Separation the variables, we get,
                          straight y space dy space equals space minus straight x space dx
    Integrating,  integral straight y space dy space equals space minus integral straight x space dx
    or                           straight y squared over 2 space equals space minus straight x squared over 2 plus straight C subscript 1 space space space or space space straight x squared plus straight y squared space equals straight c is required solution. 
    Question 180
    CBSEENMA12032992

    Solve dy over dx plus straight y space equals space 1 comma space space space straight y not equal to 1

    Solution
    The given differential equation is
    dy over dx plus straight y space equals space 1 space space space or space space space dy over dx equals space 1 minus straight y
    Separating the variables, we get,
                        fraction numerator 1 over denominator 1 minus straight y end fraction dy space equals space dx
    Integrating, integral fraction numerator 1 over denominator 1 minus straight y end fraction dy space equals space integral 1 space dx
    therefore space space space space space space fraction numerator log open vertical bar 1 minus straight y close vertical bar over denominator negative 1 end fraction space equals space straight x plus straight c apostrophe
    therefore space space space space space log space open vertical bar 1 minus straight y close vertical bar space equals space minus straight x minus straight c apostrophe
    therefore space space space space space space space space open vertical bar 1 minus straight y close vertical bar space equals space straight e to the power of negative straight x minus straight c apostrophe end exponent space space space or space space space open vertical bar 1 minus straight y close vertical bar space equals space straight e to the power of negative straight x end exponent. space straight e to the power of negative straight c apostrophe end exponent
therefore space space space space space space space space space space space 1 minus straight y space equals space plus-or-minus straight e to the power of negative straight e apostrophe end exponent space straight e to the power of negative straight x end exponent
therefore space space space space space space space space space space space space space 1 minus straight y space equals space minus ce to the power of negative straight x end exponent space space space space space space space space space space space space space space space space space space space space space space space where space minus straight c space equals space plus-or-minus straight e to the power of negative straight x end exponent
therefore space space space space space space space space space space space straight y space equals space 1 plus ce to the power of negative straight x end exponent space space is space the space required space solution. space
    Question 181
    CBSEENMA12032994

    Solve straight x to the power of 5 dy over dx space equals space minus straight y to the power of 5

    Solution

    The given differential equation is
                               straight x to the power of 5 dy over dx equals negative straight y to the power of 5 space space space space or space space space space space dy over dx space equals space minus straight y to the power of 5 over straight x to the power of 5
    Separating the variables, we get,
                                   1 over straight y to the power of 5 dy space equals space minus 1 over straight x to the power of 5 dx
    Integrating,    integral 1 over straight y to the power of 5 dy space equals space minus integral 1 over straight x to the power of 5 dx space space or space space space integral straight y to the power of negative 5 end exponent dy space equals negative integral straight x to the power of negative 5 end exponent dx
     therefore space space space space space space fraction numerator straight y to the power of negative 4 end exponent over denominator negative 4 end fraction space equals space minus fraction numerator straight x to the power of negative 4 end exponent over denominator negative 4 end fraction plus straight c apostrophe space space space space space or space space space fraction numerator 1 over denominator negative 4 straight y to the power of 4 end fraction space equals space fraction numerator 1 over denominator 4 straight x to the power of 4 end fraction plus straight c apostrophe
    or            1 over straight x to the power of 4 plus 1 over straight y to the power of 4 space equals space minus 4 straight c apostrophe
    or            straight x to the power of negative 4 end exponent plus straight y to the power of negative 4 end exponent space equals space straight c comma space space where space straight c space equals space minus 4 straight c apostrophe.

    Question 182
    CBSEENMA12032995

    Solve dy over dx space equals fraction numerator 3 straight x squared over denominator 1 plus straight y squared end fraction

    Solution
    The given differential equation is
                          dy over dx equals fraction numerator 3 straight x squared over denominator 1 plus 3 straight y squared end fraction
    Separating the variables, we get,
                      left parenthesis 1 plus 3 straight y squared right parenthesis space dy space equals space 3 straight x squared dx
    Integrating,   integral left parenthesis 1 plus 3 straight y squared right parenthesis space dy space equals space integral 3 straight x squared dx
    therefore space space space space integral 1 space dy space plus space 3 space integral straight y squared space dy space equals space 3 integral straight x squared space dx
    therefore                                straight y plus straight y cubed space equals straight x cubed plus straight c comma space space space which space is space the space required space solution.
    Question 183
    CBSEENMA12032996

    Find a one-parameter family of solutions of the following differential equations, indicating carefully the interval in which the solutions are valid
    dy over dx equals fraction numerator straight x plus 1 over denominator 2 minus straight y end fraction comma space space space space straight y space not equal to 2

    Solution
    The given differential equation is
                             dy over dx equals fraction numerator straight x plus 1 over denominator 2 minus straight y end fraction
    Separating the variables, we get,
                            left parenthesis 2 minus straight y right parenthesis space dy space equals space left parenthesis straight x plus 1 right parenthesis space dx
    Integrating,  integral left parenthesis 2 minus straight y right parenthesis space dy space equals space left parenthesis straight x plus 1 right parenthesis space dx
    therefore space space space space space space space 2 straight y minus straight y squared over 2 space equals space straight x squared over 2 plus straight x plus straight c apostrophe
    or                  4 straight y minus straight y squared space equals space straight x squared plus 2 straight x plus straight c space space space space space space where space straight c space equals space 2 straight c apostrophe
    or              straight x squared plus straight y squared plus 2 straight x minus 4 straight y plus straight c space equals space 0
    which is required solution. 
    Question 184
    CBSEENMA12032998

    Find a one-parameter family of solutions of the following differential equation, indicating carefully the interval in which the solutions are valid:
    dy over dx space equals space fraction numerator 1 plus straight y squared over denominator 1 plus straight x squared end fraction

    Solution
    The given differential equation is
                                dy over dx space equals space fraction numerator 1 plus straight y squared over denominator 1 plus straight x squared end fraction
    Separating the variables,  we get,
                          fraction numerator 1 over denominator 1 plus straight y squared end fraction dy space equals space fraction numerator 1 over denominator 1 plus straight x squared end fraction dx
    Integrating,   integral fraction numerator 1 over denominator 1 plus straight y squared end fraction dy space equals space integral fraction numerator 1 over denominator 1 plus straight x squared end fraction dx
    therefore space space space tan to the power of negative 1 end exponent straight y space equals space tan to the power of negative 1 end exponent straight x plus straight c is the solution. 
    Question 185
    CBSEENMA12033000

    Find a one-parameter family of solutions of the following differential equation, indicating carefully the interval in which the solutions are valid:
    dy over dx equals square root of 4 minus straight x squared end root comma space space minus 2 less than straight y less than 2


    Solution
    The given differential equation is
                            dy over dx equals square root of 4 minus straight y squared end root
    Separating the variables, we get,
                         fraction numerator 1 over denominator square root of 4 minus straight y squared end root end fraction dy space equals space dx
    Integrating,    integral fraction numerator 1 over denominator square root of 4 minus straight y squared end root end fraction dy space equals space integral 1 space dx
    therefore space space space integral fraction numerator 1 over denominator square root of left parenthesis 2 right parenthesis squared minus straight y squared end root end fraction dy space equals space integral 1 space dx
therefore space space sin to the power of negative 1 end exponent open parentheses straight y over 2 close parentheses space equals space straight x plus straight c
therefore space space space space space space space space space space straight y over 2 space equals space sin space left parenthesis straight x plus straight c right parenthesis
    or            straight y equals 2 space sin space left parenthesis straight x plus straight c right parenthesis comma  which is required solution.
    Question 186
    CBSEENMA12033003

    Find a one-parameter family of solutions of the following differential equation, indicating carefully the interval in which the solutions are valid:
    dy plus left parenthesis straight x plus 1 right parenthesis space left parenthesis straight y plus 1 right parenthesis space dx space equals space 0



    Solution
    The given differential equation is
                      dy plus left parenthesis straight x plus 1 right parenthesis space left parenthesis straight y plus 1 right parenthesis space dx space equals space 0 space space space space space space space space space or space space space space dy space equals space minus left parenthesis straight x plus 1 right parenthesis space left parenthesis straight y plus 1 right parenthesis space dx
    therefore space space space space space space fraction numerator 1 over denominator straight y plus 1 end fraction dy space equals space minus left parenthesis straight x plus 1 right parenthesis space dx
    Integrating,   integral fraction numerator 1 over denominator straight y plus 1 end fraction dy space equals space integral left parenthesis straight x plus 1 right parenthesis space dx
    therefore space space space log space open vertical bar straight y plus 1 close vertical bar space equals space minus open parentheses straight x squared over 2 plus straight x close parentheses space plus space straight c comma space space space straight x space element of space straight R space is space the space solution. space
    Question 187
    CBSEENMA12033006

    Find a one-parameter family of solutions of the following differential equation, indicating carefully the interval in which the solutions are valid:
    straight e to the power of straight y dx plus straight e to the power of straight x dy space equals space 0




    Solution
    The given differential equation is
            straight e to the power of straight x dx plus straight e to the power of straight x dy space equals space 0 space space space space space space space space space space space space space space space space or space space space space straight e to the power of straight x dy space equals space minus straight e to the power of straight x dx
    therefore space space space space space space straight e to the power of straight y dy space equals space minus straight e to the power of straight x dx
    Integration,  integral straight e to the power of negative straight y end exponent space dy space equals negative integral straight e to the power of negative straight x end exponent dx
    therefore space space space space space fraction numerator straight e to the power of negative straight y end exponent over denominator negative 1 end fraction space equals negative fraction numerator straight e to the power of negative straight x end exponent over denominator negative 1 end fraction plus straight c subscript 1 space or space space straight e to the power of straight y plus straight e to the power of straight x space equals space straight c comma space space straight x space element of space straight R is the solution.
    Question 188
    CBSEENMA12033008

    Find a one-parameter family of solutions of the following differential equation, indicating carefully the interval in which the solutions are valid:
    left parenthesis sinx plus cosx right parenthesis space dy space equals space left parenthesis cosx minus sinx right parenthesis space dx





    Solution
    The given differential equation is (sin x + cos x) dy = (cos x – sin x) dx
    therefore space space space space space space space dy space equals space fraction numerator cosx minus sinx over denominator sinx plus cosx end fraction dx
    Integrating,  integral 1 space dy space equals space integral fraction numerator cosx plus sinx over denominator sinx plus cosx end fraction dx
    therefore space space space space space space space space space space space space space space space space space space straight y space equals log open vertical bar sinx plus cosx close vertical bar plus straight c comma space space space straight x space element of space straight R space is space the space solution
    Question 189
    CBSEENMA12033009

    Find a one-parameter family of solutions of the following differential equation, indicating carefully the interval in which the solutions are valid:
    straight y apostrophe space equals left parenthesis 1 plus straight x squared right parenthesis thin space left parenthesis 1 plus straight y squared right parenthesis






    Solution
    The given differential equation is
                                              straight y apostrophe space equals left parenthesis 1 plus straight x squared right parenthesis thin space left parenthesis 1 plus straight y squared right parenthesis space space space space or space space space space dy over dx equals left parenthesis 1 plus straight x squared right parenthesis thin space left parenthesis 1 plus straight y squared right parenthesis
    Separating the variables, we get,
                    fraction numerator 1 over denominator 1 plus straight y squared end fraction dy space equals space left parenthesis 1 plus straight x squared right parenthesis space dx
    Integrating,   integral fraction numerator 1 over denominator 1 plus straight y squared end fraction dy space equals space integral left parenthesis 1 plus straight x squared right parenthesis space dx
    therefore space space space space space space space tan to the power of negative 1 end exponent straight y space equals space straight x plus straight x cubed over 3 plus straight c comma space space straight x space element of space straight R space is space the space solution. space
    Question 190
    CBSEENMA12033011

    Find a one-parameter family of solutions of the following differential equation, indicating carefully the interval in which the solutions are valid:
    left parenthesis straight e to the power of straight x plus straight e to the power of straight x right parenthesis space dy space minus space left parenthesis straight e to the power of straight x minus straight e to the power of straight x right parenthesis space dx space equals space 0







    Solution
    The given differential equation is
                          left parenthesis straight e to the power of straight x plus straight e to the power of negative straight x end exponent right parenthesis space dy space equals space left parenthesis straight e to the power of straight x minus straight e to the power of negative straight x end exponent right parenthesis space dx
    therefore space space space space space space space space space space space space space space space space space dy space equals space open parentheses fraction numerator straight e to the power of straight x minus straight e to the power of negative straight x end exponent over denominator straight e to the power of straight x plus straight e to the power of negative straight x end exponent end fraction close parentheses dx
    Integrating,          integral dy space equals space integral fraction numerator straight e to the power of straight x minus straight e to the power of negative straight x end exponent over denominator straight e to the power of straight x plus straight e to the power of negative straight x end exponent end fraction dx
    therefore space space space space space space space space space space space space space space space space space straight y space equals space log space left parenthesis straight e to the power of straight x plus straight e to the power of negative straight x end exponent right parenthesis space plus straight c comma space space space space straight x space element of space straight R space is space the space solution. space
    Question 191
    CBSEENMA12033014

    Solve the differential equation
    left parenthesis tan squared straight x plus 2 space tanx space plus 5 right parenthesis space dy over dx space equals space 2 left parenthesis 1 plus tanx right parenthesis space sec squared straight x.

    Solution
    The given differential equation is
                    open parentheses tan squared straight x plus 2 space tan space straight x plus 5 close parentheses space dy over dx space equals space 2 left parenthesis 1 minus tanx right parenthesis space sec squared straight x
    or        dy over dx equals space fraction numerator 2 space sec squared straight x plus 2 space tanx space sec squared straight x over denominator tan squared straight x plus 2 space tanx plus 5 end fraction
    Separating the variables,  we get,         
                          dy space equals space fraction numerator 2 space tanx space sec squared straight x space plus space 2 space sec squared straight x over denominator tan squared straight x plus 2 space tan space straight x plus 5 end fraction dx
    Integrating ,   integral 1 space dy space equals space integral fraction numerator 2 space tanx space sec squared straight x space plus space 2 sec squared straight x over denominator tan squared straight x plus 2 space tan space straight x plus 5 end fraction dx
    therefore space space space space space space space space space space space straight y equals log space open vertical bar tan squared straight x plus 2 tanx plus 5 close vertical bar space plus straight c space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space space integral fraction numerator straight f apostrophe left parenthesis straight x right parenthesis over denominator straight f left parenthesis straight x right parenthesis end fraction dx space equals space log space open vertical bar straight f left parenthesis straight x right parenthesis close vertical bar close square brackets
    which is the required solution. 
     
    Question 192
    CBSEENMA12033016

    Solve the following differential equation:
    x cos y dy = (x ex log x + ex) dx.

    Solution
    The given differential equation is
                     straight x space cos space straight y space dy space equals space left parenthesis straight x space straight e to the power of straight x space log space straight x space plus straight e to the power of straight x right parenthesis space dx
    or              cos space straight y space dy space equals space open parentheses straight e to the power of straight x logx plus straight e to the power of straight x over straight x close parentheses dx
    Integrating,     integral space cos space straight y space dy space equals space integral space straight e to the power of straight x open square brackets log space straight x space plus 1 over straight x close square brackets space dx
    therefore               space sin space straight y space equals space straight e to the power of straight x logx space plus straight c space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open curly brackets because space space space integral straight e to the power of straight x left square bracket straight f left parenthesis straight x right parenthesis plus straight f apostrophe left parenthesis straight x right parenthesis dx space equals space straight e to the power of straight x space straight f left parenthesis straight x right parenthesis close curly brackets
    which is the required solution. 
    Question 193
    CBSEENMA12033019

    Solve the following differential equation:
    dy over dx space equals space log space left parenthesis straight x plus 1 right parenthesis

    Solution
    The given differential equation is
                          dy over dx space equals space log space left parenthesis straight x plus 1 right parenthesis
    Separating the variables, we get,
                            dy space equals space log space left parenthesis straight x plus 1 right parenthesis. space dx
    Integrating,       integral dy space equals space integral log space left parenthesis straight x plus 1 right parenthesis. space 1 space dx
    therefore space space space space space space space space space space space straight y space equals space log space left parenthesis straight x plus 1 right parenthesis space. straight x space space minus space integral fraction numerator 1 over denominator straight x plus 1 end fraction straight x space dx
    or            straight y equals straight x space log left parenthesis straight x plus 1 right parenthesis minus space integral fraction numerator left parenthesis straight x plus 1 right parenthesis space minus space 1 over denominator straight x plus 1 end fraction dx
    or            straight y space equals straight x space log space left parenthesis straight x plus 1 right parenthesis space minus space integral open parentheses 1 minus fraction numerator 1 over denominator straight x plus 1 end fraction close parentheses dx
    or           straight y equals straight x space log space left parenthesis straight x plus 1 right parenthesis space minus space open square brackets straight x minus log left parenthesis straight x plus 1 right parenthesis close square brackets plus straight c
    or          straight y equals space straight x space log space left parenthesis straight x plus 1 right parenthesis space minus space straight x space plus space log space left parenthesis straight x plus 1 right parenthesis space plus straight c
    or           straight y equals left parenthesis straight x plus 1 right parenthesis space log space left parenthesis straight x plus 1 right parenthesis space minus straight x space plus straight c
    which is required solution. 
    Question 194
    CBSEENMA12033021

    Solve the following differential equation:
                left parenthesis straight y plus straight x space straight y right parenthesis space dx space plus space left parenthesis straight x minus straight x space straight y squared right parenthesis space dy space equals space 0


    Solution

    The given differential equation is
                      left parenthesis straight y plus straight x space straight y right parenthesis space dx space plus space left parenthesis straight x minus straight x space straight y squared right parenthesis space dy space equals space 0
    or space straight y left parenthesis 1 plus straight x right parenthesis space dx space plus space straight x left parenthesis 1 minus straight y squared right parenthesis space dy space equals space 0
or space space straight x left parenthesis 1 minus straight y squared right parenthesis space dy space equals space minus straight y left parenthesis 1 plus straight x right parenthesis space dx
or space fraction numerator 1 minus straight y squared over denominator straight y end fraction dy space equals space minus fraction numerator 1 plus straight x over denominator straight x end fraction dx
    Integrating,       integral fraction numerator 1 minus straight y squared over denominator straight y end fraction dy space equals space minus fraction numerator 1 plus straight x over denominator straight x end fraction dx
    therefore space space space integral open parentheses 1 over straight y minus straight y close parentheses space dy space equals space minus integral open parentheses 1 over straight x plus 1 close parentheses space dx
therefore space space log space open vertical bar straight y close vertical bar minus straight y squared over 2 space equals space minus log space straight x space minus space straight x space plus straight c comma space which space is space the space required space solution. space

    Question 195
    CBSEENMA12033024

    Solve the following differential equation:
    left parenthesis 1 minus straight x squared right parenthesis space dy space plus space straight x space straight y space dx space equals space straight x space straight y squared space dx.
                


    Solution
    The given differential equation is
                         left parenthesis 1 minus straight x squared right parenthesis space dy space plus space straight x space straight y space dx space equals space straight x space straight y squared space dx
    or                  left parenthesis 1 minus straight x squared right parenthesis space dy space equals space left parenthesis xy squared minus straight x space straight y right parenthesis space dx space space space space space space space or space space space left parenthesis 1 minus straight x squared right parenthesis space dy space equals space straight x space left parenthesis straight y squared minus straight y right parenthesis space dx
    or                 fraction numerator 1 over denominator straight y squared minus straight y end fraction dy space equals space fraction numerator straight x over denominator 1 minus straight x squared end fraction dx
    therefore space space space space space integral fraction numerator 1 over denominator straight y squared minus straight y end fraction dy space equals space integral fraction numerator straight x over denominator 1 minus straight x squared end fraction dx
therefore space space space space integral fraction numerator 1 over denominator straight y left parenthesis straight y minus 1 right parenthesis end fraction dy space equals space minus integral fraction numerator negative 2 straight x over denominator 1 minus straight x squared end fraction dx
therefore space space integral open square brackets fraction numerator 1 over denominator straight y left parenthesis 0 minus 1 right parenthesis end fraction plus fraction numerator 1 over denominator left parenthesis 1 right parenthesis space left parenthesis straight y minus 1 right parenthesis end fraction close square brackets space dy space equals space minus integral fraction numerator negative 2 straight x over denominator 1 minus straight x squared end fraction dx
therefore space integral open parentheses negative 1 over straight y plus fraction numerator 1 over denominator straight y minus 1 end fraction close parentheses space dy space equals negative integral fraction numerator negative 2 straight x over denominator 1 minus straight x squared end fraction dx
therefore space space space space minus log space open vertical bar straight y close vertical bar plus space log space open vertical bar straight y minus 1 close vertical bar space equals space minus space log space open vertical bar 1 minus straight x squared close vertical bar plus space log space straight c subscript 1
therefore space log space open vertical bar fraction numerator straight y minus 1 over denominator straight y end fraction close vertical bar plus space log space open vertical bar 1 minus straight x squared close vertical bar space equals space log space straight c subscript 1
therefore space log space open vertical bar open parentheses fraction numerator straight y minus 1 over denominator straight y end fraction close parentheses space left parenthesis 1 minus straight x squared right parenthesis close vertical bar space equals space log space straight c subscript 1 space space space space space space space space space therefore space space space space open vertical bar fraction numerator left parenthesis straight y minus 1 right parenthesis thin space left parenthesis 1 minus straight x squared right parenthesis over denominator straight y end fraction close vertical bar space equals space straight c subscript 1
therefore space space space space left parenthesis straight y minus 1 right parenthesis thin space left parenthesis 1 minus straight x squared right parenthesis space equals space straight c space straight y
    Question 196
    CBSEENMA12033025

    Solve the following differential equation:
    dy over dx space equals space 1 plus straight x plus straight y plus xy comma space space straight y greater than 0

                


    Solution
    The given differential equation is
                          dy over dx equals 1 plus straight x plus straight y plus xy space space or space space space dy over dx space equals space left parenthesis 1 plus straight x right parenthesis space plus straight y left parenthesis 1 plus straight x right parenthesis
    or             dy over dx space equals left parenthesis 1 plus straight x right parenthesis space left parenthesis 1 plus straight y right parenthesis
    Separating the variables, we get,  fraction numerator 1 over denominator 1 plus straight y end fraction dy space equals space left parenthesis 1 plus straight x right parenthesis space dx comma space space space space or space space space integral fraction numerator dy over denominator 1 plus straight y end fraction space equals space integral left parenthesis 1 plus straight x right parenthesis space dx
    therefore space space log space left parenthesis 1 plus straight y right parenthesis space equals space fraction numerator left parenthesis 1 plus straight x right parenthesis squared over denominator 2 end fraction plus straight c which is required solution. 
    Question 197
    CBSEENMA12033027

    Solve the following differential equation:
    open parentheses straight x squared straight y plus straight x squared close parentheses space dx space plus space left parenthesis straight x space straight y squared minus straight y squared right parenthesis space dy space equals space 0

                


    Solution
    The given differential equation is
                         left parenthesis straight x squared straight y plus straight x squared right parenthesis space dx plus left parenthesis straight x space straight y squared minus straight y squared right parenthesis space dy space equals space 0
    or             straight x squared left parenthesis straight y plus 1 right parenthesis space dx plus space straight y squared left parenthesis straight x minus 1 right parenthesis space dy space equals space 0 space space space space or space space space space straight y squared left parenthesis straight x minus 1 right parenthesis space dy space equals space minus straight x squared left parenthesis straight y plus 1 right parenthesis space dx
    Separating the variables, we get,
                       fraction numerator straight y squared over denominator straight y plus 1 end fraction dy space equals space minus fraction numerator straight x squared over denominator straight x minus 1 end fraction dxaa
    Integrating,  integral fraction numerator straight y squared over denominator straight y plus 1 end fraction dy space equals space minus integral fraction numerator straight x squared over denominator straight x minus 1 end fraction dx
    therefore space space space space integral open parentheses straight y minus 1 plus fraction numerator 1 over denominator straight y plus 1 end fraction close parentheses space dy space equals space minus integral open parentheses straight x plus 1 plus fraction numerator 1 over denominator straight x minus 1 end fraction close parentheses dx
therefore space space space straight y squared over 2 minus straight y plus log space open vertical bar straight y plus 1 close vertical bar space equals space open square brackets straight x squared over 2 plus straight x plus log space open vertical bar straight x minus 1 close vertical bar close square brackets space plus space straight c
    which is required solution.
    Question 198
    CBSEENMA12033029

    Solve the following differential equation:
    straight y left parenthesis 1 minus straight x squared right parenthesis dy over dx space equals space straight x left parenthesis 1 plus straight y squared right parenthesis


                


    Solution

    The given differential equation is
                           straight y left parenthesis 1 minus straight x squared right parenthesis dy over dx space equals space straight x left parenthesis 1 plus straight y squared right parenthesis
    Separating the variables, we get,
                                 fraction numerator straight y over denominator 1 plus straight y squared end fraction dy space equals space fraction numerator straight x over denominator 1 minus straight x squared end fraction dx
    Integrating,     integral fraction numerator 2 straight y over denominator 1 plus straight y squared end fraction dy space equals space minus integral fraction numerator negative 2 straight x over denominator 1 minus straight x squared end fraction dx
    therefore space space space log space space open vertical bar 1 plus straight y squared close vertical bar space equals space minus log space open vertical bar 1 minus straight x squared close vertical bar plus log space straight c
therefore space space log space open vertical bar 1 minus straight x squared close vertical bar plus log open vertical bar 1 plus straight y squared close vertical bar space equals space log space straight c
therefore space space log space open vertical bar 1 minus straight x squared close vertical bar plus log space open vertical bar 1 plus straight y squared close vertical bar space equals space log space straight c
therefore space log space open vertical bar left parenthesis 1 minus straight x squared right parenthesis thin space left parenthesis 1 plus straight y squared right parenthesis close vertical bar space equals space log space straight c
therefore space space space open vertical bar left parenthesis 1 minus straight x squared right parenthesis thin space left parenthesis 1 plus straight y squared right parenthesis close vertical bar space equals space straight c
therefore space space left parenthesis 1 minus straight x squared right parenthesis thin space left parenthesis 1 plus straight y squared right parenthesis space equals space straight A comma space where space straight A space is space constant.
    This is required solution. 

    Question 199
    CBSEENMA12033030

    Find the general solution of each of the following equations
    dy over dx equals straight x to the power of 5 plus straight x squared minus 2 over straight x

    Solution

    The given differential equation is
            dy over dx space equals space straight x to the power of 5 plus straight x squared minus 2 over straight x
    Separating the variables, we get, dy space equals space open parentheses straight x to the power of 5 plus straight x squared minus 2 over straight x close parentheses dx
    Integrating, we get,    straight y equals straight x to the power of 6 over 3 plus straight x cubed over 3 minus 2 space log space open vertical bar straight x close vertical bar space plus space straight c
    where c is an arbitrary constant. 

    Question 200
    CBSEENMA12033031

    Find the general solution of each of the following equations:
    left parenthesis straight x plus 2 right parenthesis space dy over dx space equals space straight x squared plus 4 straight x minus 9


    Solution
    The given differential equation is
                 left parenthesis straight x plus 2 right parenthesis space dy over dx space equals space straight x squared plus 4 straight x minus 9    or    dy over dx space equals space fraction numerator straight x squared plus 4 straight x minus 9 over denominator straight x plus 2 end fraction
    Separating the variables, we get
                               dy space equals space open parentheses fraction numerator straight x squared plus 4 straight x minus 9 over denominator straight x plus 2 end fraction close parentheses space dx
    or                 dy space equals open parentheses fraction numerator straight x squared plus 4 straight x minus 9 over denominator straight x plus 2 end fraction close parentheses dx
    or         dy space equals space open parentheses straight x plus 2 minus fraction numerator 13 over denominator straight x plus 2 end fraction close parentheses dx
    Integrating, 
                   straight y equals straight x squared over 2 plus 2 straight x minus 13 space log space open vertical bar straight x plus 2 close vertical bar space plus space straight c
    which is required solution. 
                                          straight x plus 2 space space fraction numerator straight x plus 2 over denominator long division enclose straight x squared plus 4 straight x minus 9 end enclose end fraction
space space space space space space space space space space space space space space space space straight x squared plus 2 straight x
space space space space space space space space space space space space space space space space minus space space minus
space space space space space space space space space space space space space _________
space space space space space space space space space space space space space 2 straight x space space minus space 9
space space space space space space space space space space space space space 2 straight x space plus space 4
space space space space space space space space space space space space space space minus
space space space space space space space space space space space space space _________
space space space space space space space space space space space space space space space space space space space space space space space space 13





    Question 201
    CBSEENMA12033032

    Find the general solution of each of the following equations:
    dy over dx plus 2 straight x equals space straight e to the power of 3 straight x end exponent



    Solution
    The given differential equation is
                     dy over dx plus 2 straight x space equals space straight e to the power of 3 straight x end exponent space space space space or space space space space dy over dx space equals space straight e to the power of 3 straight x end exponent space minus space 2 straight x
    Separating the variables, we get, dy space equals space left parenthesis straight e to the power of 3 straight x end exponent minus 2 straight x right parenthesis space dx
    Integrating, straight y space equals space straight e to the power of 3 straight x end exponent over 3 minus 2 straight x squared over 2 space equals space straight c space space space or space space space space straight y space equals space 1 third space straight e to the power of 3 straight x end exponent space minus space straight x squared plus straight c comma space is space the space required space solution.
    Question 202
    CBSEENMA12033033

    Find the general solution of each of the following equations:
    dy over dx equals fraction numerator straight y left parenthesis straight x squared minus 1 right parenthesis over denominator straight x left parenthesis straight y squared minus 1 right parenthesis end fraction





    Solution

    The given differential equation is
                 dy over dx space equals space fraction numerator straight y left parenthesis straight x squared minus 1 right parenthesis over denominator straight x left parenthesis straight y squared minus 1 right parenthesis end fraction
    Separating the variables, we get,
                              fraction numerator straight y squared minus 1 over denominator straight y end fraction dy space equals space fraction numerator straight x squared minus 1 over denominator straight x end fraction dx
    therefore space space space space space space integral open parentheses straight y squared over straight y minus 1 over straight y close parentheses dy space equals space integral open parentheses straight x squared over straight x minus 1 over straight x close parentheses dx
    or          integral open parentheses straight y minus 1 over straight y close parentheses dy space equals space integral open parentheses straight x minus 1 over straight x close parentheses dx
    or        straight y squared over 2 minus log space open vertical bar straight y close vertical bar space equals space straight x squared over 2 minus log space open vertical bar straight x close vertical bar space plus space straight c
    is the required solution. 

    Question 203
    CBSEENMA12033034

    Find the general solution of each of the following equation:
    left parenthesis straight x minus 1 right parenthesis space straight y apostrophe space equals space 2 space straight x cubed space straight y space where space straight y apostrophe space equals space dy over dx






    Solution
    The given differential equation is
                    left parenthesis straight x minus 1 right parenthesis space straight y apostrophe space equals space space 2 straight x cubed straight y
    or     open parentheses straight x minus 1 close parentheses space dy over dx space equals space 2 straight x cubed straight y space space space space space space space space space space space space space or space space space space space dy over dx space equals space fraction numerator 2 straight x cubed straight y over denominator straight x minus 1 end fraction.
    Separating the variables, we get,
                        right enclose table row cell 1 over straight y dy space equals space fraction numerator 2 straight x cubed over denominator straight x minus 1 end fraction dx end cell row cell or space space 1 over straight y dy space equals space open parentheses 2 straight x squared plus 2 straight x plus 2 plus fraction numerator 2 over denominator straight x minus 1 end fraction close parentheses dx end cell row cell table row cell Integrating comma space we space get comma end cell row cell log space open vertical bar straight y close vertical bar space equals space 2 straight x cubed over 3 plus fraction numerator 2 straight x squared over denominator 2 end fraction plus 2 straight x end cell row cell table row cell plus 2 space log space open vertical bar straight x minus 1 close vertical bar plus straight A end cell row cell or space log space open vertical bar straight y close vertical bar minus 2 space log space open vertical bar straight x minus 1 close vertical bar end cell row cell equals 2 over 3 straight x cubed plus straight x squared plus 2 straight x plus straight A end cell end table end cell end table end cell end table end enclose space table row cell table row cell table row cell table row cell stack straight x minus 1 long division enclose space 2 straight x cubed end enclose with 2 straight x squared plus 2 straight x plus 2 on top end cell row cell space space space space space space 2 straight x cubed minus 2 straight x squared end cell row cell negative space space plus space end cell end table end cell row _________ row cell 2 space straight x squared end cell end table end cell row cell 2 straight x squared minus 2 straight x end cell row cell negative space space space plus end cell end table end cell row ___________ row cell table row cell 2 space straight x end cell row cell 2 straight x minus 2 end cell row cell table row cell negative space plus end cell row __________ row 2 end table end cell end table end cell end table




space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space
    or  log space open vertical bar fraction numerator straight y over denominator left parenthesis straight x minus 1 right parenthesis squared end fraction close vertical bar space equals 2 over 3 straight x cubed plus straight x squared plus 2 straight x plus straight A space space space space space space rightwards double arrow space space space open vertical bar fraction numerator straight y over denominator left parenthesis straight x minus 1 right parenthesis squared end fraction close vertical bar space equals space straight e to the power of 2 over 3 straight x cubed plus straight x squared plus 2 straight x plus straight A end exponent
    or                  straight y space equals straight e to the power of straight x space left parenthesis straight x minus 1 right parenthesis squared space straight e to the power of 2 over 3 straight x cubed plus straight x squared plus 2 straight x end exponent space space space space or space space space space straight y space equals straight e space left parenthesis straight x minus 1 right parenthesis squared space straight e to the power of 2 over 3 straight x cubed plus straight x squared plus 2 straight x end exponent
    where e is an arbitrary constant. 
    Question 204
    CBSEENMA12033035

    Find the general solution of the differential equation:
    dy over dx plus square root of fraction numerator 1 minus straight y squared over denominator 1 minus straight x squared end fraction end root space equals space 0.

    Solution
    The given differential equation is
                       dy over dx plus square root of fraction numerator 1 minus straight y squared over denominator 1 minus straight x squared end fraction end root space equals space 0
    or           dy over dx space equals space minus fraction numerator square root of 1 minus straight y squared end root over denominator square root of 1 minus straight x squared end root end fraction comma space space or space space space fraction numerator 1 over denominator square root of 1 minus straight y squared end root end fraction dy space equals space minus fraction numerator 1 over denominator square root of 1 minus straight x squared end root end fraction dx
    Integrating both sides, w.r.t. x,
                     integral fraction numerator 1 over denominator square root of 1 minus straight y squared end root end fraction dy space equals space minus integral fraction numerator 1 over denominator square root of 1 minus straight x squared end root end fraction dx
    therefore space sin to the power of negative 1 end exponent straight y space equals space minus sin to the power of negative 1 end exponent space straight x space plus space sin to the power of negative 1 end exponent straight c comma space space where space sin to the power of negative 1 end exponent straight c space is an arbitrary constant. 
    therefore space space space space sin to the power of negative 1 end exponent straight x plus sin to the power of negative 1 end exponent straight y space equals space sin to the power of negative 1 end exponent straight c
    rightwards double arrow space space space space sin to the power of negative 1 end exponent open square brackets straight x square root of 1 minus straight y squared end root plus straight y square root of 1 minus straight x squared end root close square brackets space equals space sin to the power of negative 1 end exponent straight c
    or        straight x square root of 1 minus straight y squared end root plus straight y square root of 1 minus straight x squared end root space equals space straight c comma space where c is an arbitrary constant. 
    Question 205
    CBSEENMA12033036

    Find a one parameter family of solutions of each of the following differential equation:
    y' = ex + y + e–x + y

    Solution
    The given differential equation is
                                   dy over dx equals space straight e to the power of straight x plus straight y end exponent space plus space straight e to the power of negative straight x plus straight y end exponent space space space space space or space space space space dy over dx space equals space straight e to the power of straight x. space straight e to the power of straight y space plus space straight e to the power of straight x. space straight e to the power of straight y
    or                   dy over dx space equals space straight e to the power of straight y left parenthesis straight e to the power of straight x minus straight e to the power of straight x right parenthesis
    Separating the variables and integrating, we get,
                                  integral straight e to the power of negative straight y end exponent dy space equals space integral left parenthesis straight e to the power of straight x plus straight e to the power of negative straight x end exponent right parenthesis space dx
    therefore space space space space space space space space space space fraction numerator straight e to the power of negative straight y end exponent over denominator negative 1 end fraction space equals space straight e to the power of straight x plus fraction numerator straight e to the power of negative straight x end exponent over denominator negative 1 end fraction plus straight c space space space space space space space or space space space minus straight e to the power of straight y space equals space straight e to the power of straight x. end exponent space straight e to the power of negative straight x end exponent plus straight c
    is the required solutions. 
    Question 206
    CBSEENMA12033037

    Find a one parameter family of solutions of each of the following differential equation:
    y' = (cos2x – sin2x) cos2 y

    Solution
    The given differential equation is
                            dy over dx space equals space left parenthesis cos squared straight x minus sin squared straight x right parenthesis space cos squared straight y
    Separating the variables, we get,
                               fraction numerator 1 over denominator cos squared straight y end fraction dy space equals space left parenthesis cos squared straight x minus sin squared straight x right parenthesis space dx
    Integrating,     integral sec squared straight y space dy space equals space integral cos space 2 straight x space dx
    therefore space space space space space space space space space tan space straight y space equals space fraction numerator sin space 2 straight x over denominator 2 end fraction plus straight c is the required solution. 
    Question 207
    CBSEENMA12033038

    Find a one parameter family of solutions of each of the following differential equation:
     (x y2 + 2x) dx + (x2 y + 2y) dy = 0

    Solution

    The given differential equation is
                    (x y2 + 2x) dx + (x2 y + 2y) dy = 0
    or       straight y left parenthesis straight x squared plus 2 right parenthesis space dx space equals space minus straight x left parenthesis straight y squared plus 2 right parenthesis space dx
    therefore space space space space space fraction numerator straight y over denominator straight y squared plus 2 end fraction dy space equals negative fraction numerator straight x over denominator straight x squared plus 2 end fraction dx
    Integrating, integral fraction numerator 2 straight y over denominator straight y squared plus 2 end fraction dy space equals negative integral fraction numerator 2 straight x over denominator straight x squared plus 2 end fraction dx
    therefore space space space space space space log space left parenthesis straight y squared plus 2 right parenthesis space equals space minus log left parenthesis straight x squared plus 2 right parenthesis space plus space log space straight c space space space or space space space log space open square brackets left parenthesis straight y squared plus 2 right parenthesis space left parenthesis straight x squared plus 2 right parenthesis close square brackets space plus space log space straight c
therefore space space space space left parenthesis straight y squared plus 2 right parenthesis thin space left parenthesis straight x squared plus 2 right parenthesis space equals space straight c space is space the space required space solution.   

    Question 208
    CBSEENMA12033039

    Find a one parameter family of solutions of each of the following differential equation:
    x y y' = 1 + x + y + x y

    Solution
    The given differential equation is
                     straight x space straight y space dy over dx space equals space 1 plus straight x plus straight y plus xy space space space space space space space space space or space space space space straight x space straight y dy over dx space equals space left parenthesis 1 plus straight x right parenthesis plus straight y left parenthesis 1 plus straight x right parenthesis
    or              straight x space straight y dy over dx space equals space left parenthesis 1 plus straight x right parenthesis thin space left parenthesis 1 plus straight y right parenthesis
    Separating the varibles, we get,
                                fraction numerator straight y over denominator 1 plus straight y end fraction dy space equals space fraction numerator 1 plus straight x over denominator straight x end fraction dx space space space space space space space or space space space space space space space space space integral fraction numerator straight y space dy over denominator 1 plus straight y end fraction space equals space integral fraction numerator 1 plus straight x over denominator straight x end fraction dx
    therefore space space space space space integral open parentheses 1 minus fraction numerator 1 over denominator 1 plus straight y end fraction close parentheses space dy space equals space integral open parentheses 1 over straight x plus 1 close parentheses space dx
therefore space space space straight y minus log space left parenthesis 1 plus straight y right parenthesis space equals space log space straight x space plus straight x space plus straight c comma space which space is space required space solution. space
    Question 209
    CBSEENMA12033040

    Solve:
    dy over dx equals straight e to the power of straight x minus straight y end exponent plus straight x squared straight e to the power of straight y

    Solution
    dy over dx equals straight e to the power of straight x minus straight y end exponent plus straight x squared straight e to the power of straight x space space space space rightwards double arrow space space space space dy over dx space equals space straight e to the power of straight x. space straight e to the power of straight y plus space straight x squared. space straight e to the power of straight y.
    rightwards double arrow space space space space space space space dy over dx space equals space left parenthesis straight e to the power of straight x plus straight x squared right parenthesis space straight e to the power of straight y
    Separating the variables, we get,
                              dy over straight e to the power of negative straight y end exponent space equals space left parenthesis straight e to the power of straight x plus straight x squared right parenthesis dx space space rightwards double arrow space space space integral straight e to the power of straight y space dy space space equals space integral left parenthesis straight e to the power of straight x plus straight x squared right parenthesis space dx
    therefore space space space space straight e to the power of straight y space equals space straight e to the power of straight x plus straight x cubed over 3 plus straight c which is the required solution.
    Question 210
    CBSEENMA12033041

    Solve:
    dy over dx space equals straight e to the power of straight x plus straight y end exponent plus straight x squared space straight e to the power of straight y.

    Solution
    dy over dx space equals straight e to the power of straight x plus straight y end exponent plus straight x squared straight e to the power of straight y space space space rightwards double arrow space space space dy over dx equals space straight e to the power of straight x. space space straight e to the power of straight y plus space straight x squared space straight e to the power of straight y space space space space rightwards double arrow space space dy over dx equals space left parenthesis straight e to the power of straight x plus straight x squared right parenthesis space straight e to the power of straight y
    Separating the variables,  we get,   dy over straight e to the power of straight y space equals space left parenthesis straight e to the power of straight x plus straight x squared right parenthesis space dx
    therefore space space space space integral straight e to the power of negative straight y end exponent dy space equals space integral left parenthesis straight e to the power of straight x plus straight x squared right parenthesis space dx space space space rightwards double arrow space space space space fraction numerator straight e to the power of negative straight y end exponent over denominator negative 1 end fraction space equals straight e to the power of straight x plus straight x cubed over 3 plus straight c
    or   straight e to the power of negative straight y end exponent plus straight e to the power of straight x plus straight x cubed over 3 plus straight c space equals space 0 which is the required solution.
    Question 211
    CBSEENMA12033042

    Solve:
    dy over dx space equals straight e to the power of straight x minus straight y end exponent plus straight x cubed straight e to the power of negative straight y end exponent

    Solution

    The given differential equation is   
                        dy over dx space equals space straight e to the power of straight x minus straight y end exponent plus straight x cubed straight e to the power of negative straight y end exponent space space or space space dy over dx space equals space straight e to the power of straight x. space straight e to the power of negative straight y end exponent space plus space straight x cubed. straight e to the power of negative straight y end exponent space space or space space dy over dx space equals space left parenthesis straight e to the power of straight x plus straight x cubed right parenthesis space straight e to the power of negative straight y end exponent
    Separating the variables, we get,  1 over straight e to the power of negative straight y end exponent dy space equals space left parenthesis straight e to the power of straight x plus straight x cubed right parenthesis space dx
    rightwards double arrow space space space integral straight e to the power of straight y space dy space equals space integral left parenthesis straight e to the power of straight x plus straight x cubed right parenthesis space dx space space rightwards double arrow space space space straight e to the power of straight y space equals space straight e to the power of straight x plus straight x to the power of 4 over 4 plus straight c is the required solution.

    Question 212
    CBSEENMA12033043

    Solve:
    x (1 + y2) dx + y (1 + x2)dy = 0  

    Solution

    The given differential equation is
    x(1 + y2) dx + y(1 + x2)dy = 0  
    therefore space space space space straight y left parenthesis 1 plus straight x squared right parenthesis space dy equals space minus straight x left parenthesis 1 plus straight y squared right parenthesis space dx
therefore space space space space space fraction numerator straight y over denominator 1 plus straight x squared end fraction dy space equals space minus fraction numerator straight x over denominator 1 plus straight x squared end fraction dx
    Integrating, integral fraction numerator straight y over denominator 1 plus straight y squared end fraction dy space equals space minus integral fraction numerator straight x over denominator 1 plus straight x squared end fraction dx
    therefore space space space space integral fraction numerator 2 straight y over denominator 1 plus straight y squared end fraction dy plus integral fraction numerator 2 straight x over denominator 1 plus straight x squared end fraction dx space equals space 0
    therefore space space space log space left parenthesis 1 plus straight y squared right parenthesis plus space log space left parenthesis 1 plus straight x squared right parenthesis space equals space log space straight c
therefore space space log space left parenthesis 1 plus straight x squared right parenthesis thin space left parenthesis 1 plus straight y squared right parenthesis space equals space log space straight c
therefore space space left parenthesis 1 plus straight x squared right parenthesis thin space left parenthesis 1 plus straight y squared right parenthesis space equals straight c
    which is required solution. 

    Question 213
    CBSEENMA12033044

    Solve:
    (1 + x) (1 + y2) dx + (1 + y) (1 + x2) dy = 0.

    Solution
    The given differential equation is
                 (1 + x) (1 + y2) dx + (1 + y) (1 + x2) dy = 0
    or             left parenthesis 1 plus straight x right parenthesis space left parenthesis 1 plus straight y squared right parenthesis space dx space equals space minus left parenthesis 1 plus straight y right parenthesis thin space left parenthesis 1 plus straight x squared right parenthesis space dy
    or           fraction numerator 1 plus straight y over denominator 1 plus straight y squared end fraction dy space equals space minus fraction numerator 1 plus straight x over denominator 1 plus straight x squared end fraction dx space space space rightwards double arrow space space space integral fraction numerator 1 plus straight y over denominator 1 plus straight y squared end fraction dy space equals space minus integral fraction numerator 1 plus straight x over denominator 1 plus straight x squared end fraction dx
    therefore space space space space integral fraction numerator 1 over denominator 1 plus straight y squared end fraction dy plus 1 half integral fraction numerator 2 straight y over denominator 1 plus straight y squared end fraction dy space equals space minus integral fraction numerator 1 over denominator 1 plus straight x squared end fraction dx minus 1 half integral fraction numerator 2 straight x over denominator 1 plus straight x squared end fraction dx
therefore space space space space space tan to the power of negative 1 end exponent straight y space plus space 1 half space log space left parenthesis 1 plus straight y squared right parenthesis space equals space minus tan to the power of negative 1 end exponent straight x space minus space 1 half log left parenthesis 1 plus straight x squared right parenthesis space plus straight c
    or         tan to the power of negative 1 end exponent straight x plus tan to the power of negative 1 end exponent straight y plus 1 half open square brackets log space left parenthesis 1 plus straight x squared right parenthesis space plus space log space left parenthesis 1 plus straight y squared right parenthesis close square brackets space equals space straight c
    or            tan to the power of negative 1 end exponent straight x plus tan to the power of negative 1 end exponent straight y plus 1 half log space open square brackets left parenthesis 1 plus straight x squared right parenthesis thin space left parenthesis 1 plus straight y squared right parenthesis close square brackets space equals space straight c space is space the space required space solution. space
    Question 214
    CBSEENMA12033045

    For the following differential equation, find the general solution:
    dy over dx equals fraction numerator 1 minus cosx over denominator 1 plus cosx end fraction

    Solution
    The given differential equation is
                         dy over dx space equals space fraction numerator 1 minus cosx over denominator 1 plus cosx end fraction
    or         dy space equals space fraction numerator 1 minus cosx over denominator 1 plus cosx end fraction dx space space space or space space space space integral dy space equals space fraction numerator 1 minus cosx over denominator 1 plus cosx end fraction dx
    therefore space space space space space integral dy space equals space integral fraction numerator 2 space sin squared begin display style straight x over 2 end style over denominator 2 space cos squared space begin display style straight x over 2 end style end fraction dx space space or space space space integral space 1. space dy space equals space integral tan squared straight x over 2 dx
    or     integral 1. space dy space equals space integral open parentheses sec squared straight x over 2 minus 1 close parentheses space dx comma space space or space space space straight y space equals space fraction numerator tan begin display style straight x over 2 end style over denominator begin display style 1 half end style end fraction minus straight x plus straight c
    or       straight y space equals space 2 space tan straight x over 2 minus straight x plus straight c which is the required solution. 
    Question 215
    CBSEENMA12033046

    For the following differential equation, find the general solution:
    dy over dx space equals sin to the power of negative 1 end exponent straight x

    Solution
    The given differential equation is
                        dy over dx space equals space sin to the power of negative 1 end exponent straight x
    Separating the variables and integrating,
                           integral space dy space equals space integral space sin to the power of negative 1 end exponent straight x space dx
    therefore space space space space space space space space space space space space integral space 1 space dy space equals space integral space sin to the power of negative 1 end exponent straight x. space 1 space dx
therefore space space space space space space space space space space straight y space equals space left parenthesis sin to the power of negative 1 end exponent straight x right parenthesis. space straight x space minus space space integral fraction numerator 1 over denominator square root of 1 minus straight x squared end root end fraction. straight x space dx
or space space space space space space space space space space space space space space space space space space space straight y space equals space straight x space sin to the power of negative 1 end exponent straight x space plus space 1 half integral left parenthesis 1 minus straight x squared right parenthesis to the power of negative 1 half end exponent left parenthesis negative 2 space straight x right parenthesis space dx
therefore space space space space space space space space space space space space space space space space space space space straight y space equals space straight x space sin to the power of negative 1 end exponent straight x space plus space 1 half fraction numerator left parenthesis 1 minus straight x squared right parenthesis to the power of begin display style 1 half end style end exponent over denominator begin display style 1 half end style end fraction plus straight c
therefore space space space space space space space space space space space space space space space space space space space space straight y space equals space straight x space sin to the power of negative 1 end exponent straight x space plus space square root of 1 minus straight x squared end root plus straight c
    which is the required solution.
    Question 216
    CBSEENMA12033047

    Solve 3ex tan y dx + (1 + ex) sec2 y dy = 0. 

    Solution
    The given differential equation is
                       3ex tan y dx + (1 + ex) sec2 y dy = 0
         or       left parenthesis 1 plus straight e to the power of straight x right parenthesis space sec squared straight y space dy space equals space minus space 3 space straight e to the power of straight x space tan space straight y space dx
    or            fraction numerator sec squared straight y over denominator tan space straight y end fraction dy space equals space minus 3 fraction numerator straight e to the power of straight x over denominator 1 plus straight e to the power of straight x end fraction dx
    Integrating, 
                                integral fraction numerator sec squared straight y over denominator tan space straight y end fraction dy space equals space minus 3 space integral fraction numerator straight e to the power of straight x over denominator 1 plus straight e to the power of straight x end fraction dx
    therefore space space space space log space open vertical bar tan space straight y close vertical bar space equals space minus 3 space log space left parenthesis 1 plus straight e to the power of straight x right parenthesis space plus space straight c comma which is required solution..
    Question 217
    CBSEENMA12033048

     Solve 4 ex tan y dx + 3(1 + e) secy dy = 0. 

    Solution
    The given differential equation is 4 ex tan y dx + 3(1 + ex ) sec2 y dy = 0.
    therefore space space 3 space left parenthesis 1 plus straight e to the power of straight x right parenthesis space sec squared straight y space dy space equals negative space 4 space straight e to the power of straight x space tan space straight y space dx
    or    fraction numerator sec squared straight y over denominator tan space straight y end fraction dy space equals space minus 4 over 3 fraction numerator straight e to the power of straight x over denominator 1 plus straight e to the power of straight x end fraction dx
    therefore space space space space integral fraction numerator sec squared straight y over denominator tan space straight y end fraction dy space equals space minus 4 over 3 integral fraction numerator straight e to the power of straight x over denominator 1 plus straight e to the power of straight x end fraction dx
    therefore space space log space open vertical bar tan space straight y close vertical bar space equals negative 4 over 3 space log space left parenthesis 1 plus straight e to the power of straight x right parenthesis space plus space log space straight c
therefore space log space open vertical bar tan space straight y close vertical bar space equals space log space left parenthesis 1 plus straight e to the power of straight x right parenthesis to the power of fraction numerator negative 4 over denominator 3 end fraction end exponent space plus space log space straight c. space space space space space therefore space space space log space open vertical bar tan space straight y close vertical bar space equals space log space fraction numerator straight c over denominator left parenthesis 1 plus straight e to the power of straight x right parenthesis to the power of begin display style 4 over 3 end style end exponent end fraction
therefore space space space space space open vertical bar tan space straight y close vertical bar space equals fraction numerator straight c over denominator left parenthesis 1 plus straight e to the power of straight x right parenthesis to the power of begin display style 4 over 3 end style end exponent end fraction space is space the space required space solution. space
                 
    Question 218
    CBSEENMA12033049

    For the following differential equation, find the general solution:
    sec2 x tan y dx – sec2 y tan x dy = 0.

    Solution
    The given differential equation is
                    sec2 x tan y dx – sec2 y tan x dy = 0.
    or    sec2 x tan y dx = sec2y tan x dy 
    or     fraction numerator sec squared straight y over denominator tan space straight y end fraction dy space equals space fraction numerator sec squared straight x over denominator tan space straight x end fraction dx
    Integrating,  we get,
                    integral fraction numerator sec squared straight y over denominator tan space straight y end fraction dy space equals space integral fraction numerator sec squared straight x over denominator tanx end fraction dx
    or      log space open vertical bar tan space space straight y close vertical bar space equals space log space open vertical bar space tan space straight x close vertical bar space plus space log space straight A
    or space space log space open vertical bar tan space straight y close vertical bar space minus space log space open vertical bar tan space straight x close vertical bar space equals space log space straight A
or space space log space open parentheses fraction numerator open vertical bar tan space straight y close vertical bar over denominator open vertical bar tan space straight x close vertical bar end fraction close parentheses space equals space log space space straight A space space space space space space space space space space space space space space space space space space space space space space space space or space space space log space open vertical bar fraction numerator tan space straight y over denominator tan space straight x end fraction close vertical bar space equals space log space straight A
or space space space space space space space space space space open vertical bar fraction numerator tan space straight y over denominator tan space straight x end fraction close vertical bar space equals straight A space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space or space space space space fraction numerator tan space straight y over denominator tan space straight x end fraction space equals space plus-or-minus space straight A
or space space space space space fraction numerator tan space straight y over denominator tan space straight x end fraction space equals straight c comma space space space where space straight c space is space arbitrary space constant. space
or space space space space space tan space straight y space equals space straight c space tanx space comma space which space is space required space solution. space
    Question 219
    CBSEENMA12033050

    For the following differential equation, find the general solution:
    sec2 x tan y dx + sec2 y tan x dy = 0.

    Solution
    The given differential equation is
                          sec2 x tan y dx + sec2 y tan x dy = 0
     or            sec squared straight y space tanx space dy space equals space sec squared straight x space tan space straight y space dx
    Separating the variables, we get,
                                   fraction numerator sec squared over denominator tan space straight y end fraction dy space equals space minus fraction numerator sec squared straight x over denominator tan space straight x end fraction dx
    Integrating,   log space open vertical bar tan space straight y close vertical bar space equals space minus log space open vertical bar tan space straight x close vertical bar space plus space log space straight A
    or   log space open vertical bar tan space straight y close vertical bar space plus space log space open vertical bar tan space straight x close vertical bar space equals space log space straight A space or space log space open vertical bar tan space straight x space tany close vertical bar space equals space log space straight A
    or   open vertical bar tan space straight x space tan space straight y close vertical bar space equals space straight A space space space space space space rightwards double arrow space space space tan space straight x space tan space straight y space equals space plus-or-minus straight A space space space or space space space tanx space tany space equals space straight c
    where c is an arbitrary constant. 
    Question 220
    CBSEENMA12033051

    Solve:
    3ex tan y dx + (1 – ex) sec2y dy = 0.

    Solution

    The given differential equation is
              3ex tan y dx + (1 – ex) sec2y dy = 0
    or    left parenthesis 1 minus straight e to the power of straight x right parenthesis space sec squared straight y space dy space equals negative 3 space straight e to the power of straight x space tan space straight y space dx space space space or space space space fraction numerator sec squared straight y over denominator tan space straight y end fraction dy space equals space minus 3 fraction numerator straight e to the power of straight x over denominator 1 minus straight e to the power of straight x end fraction dx
    therefore space space space space integral fraction numerator sec squared straight y over denominator tan space straight y end fraction dy space equals 3 integral fraction numerator straight e to the power of negative straight x end exponent over denominator 1 minus straight e to the power of straight x end fraction dx space space space space space space space rightwards double arrow space space space space log space left parenthesis tan space straight y right parenthesis space equals space 3 space log space left parenthesis 1 minus straight e to the power of straight x right parenthesis space plus space log space straight c
    therefore space space space log space left parenthesis tan space straight y right parenthesis space equals space log space left parenthesis 1 minus straight e to the power of straight x right parenthesis cubed plus space log space straight c space space space space rightwards double arrow space space space log space left parenthesis tany right parenthesis space equals space log space open square brackets straight e left parenthesis 1 minus straight e to the power of straight x right parenthesis cubed close square brackets
therefore space space space tan space straight y space equals space straight e left parenthesis 1 minus straight e to the power of straight x right parenthesis cubed space is space the space required space solution. space

    Question 221
    CBSEENMA12033052

    Solve:
     ex tan y dx + (1 – ex) sec2 y dy = 0.

    Solution

    The given differential equation is
                               straight e to the power of straight x space tany space dx space plus space left parenthesis 1 minus straight e to the power of straight x right parenthesis space sec squared straight y space dy space equals space 0
    or          left parenthesis 1 minus straight e to the power of straight x right parenthesis space sec squared straight y space dy space equals space minus straight e to the power of straight x space tan space straight y space dx space space space or space space space fraction numerator sec squared straight y over denominator tan space straight y end fraction space dy space equals space minus fraction numerator straight e to the power of straight x over denominator 1 minus straight e to the power of straight x end fraction dx
    therefore space space space integral fraction numerator sec squared straight y over denominator tan space straight y end fraction dy space equals space integral fraction numerator negative straight e to the power of straight x over denominator 1 minus straight e to the power of straight x end fraction dx
rightwards double arrow space space space space log space left parenthesis tan space straight y right parenthesis space equals space log space left parenthesis 1 minus straight e to the power of straight x right parenthesis space plus space log space straight e
rightwards double arrow space space space space log space left parenthesis tan space straight y right parenthesis space equals space log space left square bracket straight e space left parenthesis 1 minus straight e to the power of straight x right parenthesis right square bracket
therefore space space space space space space space tan space straight y space equals space straight e left parenthesis 1 minus straight e to the power of straight x right parenthesis space is space the space required space solution. space space

    Question 222
    CBSEENMA12033053

    Solve:
    tan y dx + sec2 y tan x dy = 0. 

    Solution
    The given differential equation is
              tan y dx + sec2 y tan x dy = 0  or   sec2 y tan x dy  = - tan y dx
    Separating the variables, we get,
                       fraction numerator sec squared straight y over denominator tan space straight y end fraction dy space equals space minus fraction numerator 1 over denominator tan space straight x end fraction dx
    Integrating,   integral fraction numerator sec squared straight y over denominator tan space straight y end fraction dy space equals negative fraction numerator 1 over denominator tan space straight x end fraction dx
    therefore space space log space open vertical bar tan space straight y close vertical bar space equals space minus log space open vertical bar sin space straight x close vertical bar space plus space log space straight c apostrophe
therefore space space log space open vertical bar tan space straight y close vertical bar space plus space log space open vertical bar sin space straight x close vertical bar space equals space log space straight c apostrophe
therefore space space log space open vertical bar tan space straight y space sinx space close vertical bar space equals space log space straight c apostrophe
therefore space space open vertical bar tany space sinx close vertical bar space equals space straight c apostrophe
therefore space space tany space sinx space space equals space straight A comma space where space straight A space is space constant. space
    Question 223
    CBSEENMA12033054

    Solve:
     left parenthesis 1 plus straight y squared right parenthesis thin space left parenthesis 1 plus log space straight x right parenthesis space dx space plus space straight x space dy space equals space 0

    Solution

    The given differential equation is
                       left parenthesis 1 plus straight y squared right parenthesis thin space left parenthesis 1 plus log space straight x right parenthesis space dx space plus space straight x space dy space equals space 0 space space or space space straight x space dy space equals space minus left parenthesis 1 plus straight y squared right parenthesis thin space left parenthesis 1 plus space log space straight x right parenthesis space dx
    Separating the variables, we get,
                   fraction numerator dy over denominator 1 plus straight y squared end fraction space equals negative fraction numerator 1 plus log space straight x over denominator straight x end fraction dx
    Integrating,   integral fraction numerator 1 over denominator 1 plus straight y squared end fraction dy space equals space minus integral left parenthesis 1 plus log space straight x right parenthesis. space 1 over straight x dx
    therefore space space space tan to the power of negative 1 end exponent straight y space plus straight c space equals space minus fraction numerator left parenthesis 1 plus space log space straight x right parenthesis squared over denominator 2 end fraction space space space space space open square brackets because space space integral open square brackets straight f left parenthesis straight x right parenthesis close square brackets to the power of straight n space straight f apostrophe left parenthesis straight x right parenthesis space dx space equals space fraction numerator straight f to the power of straight n plus 1 end exponent left parenthesis straight x right parenthesis over denominator straight n plus 1 end fraction plus straight c close square brackets
therefore space space space tan to the power of negative 1 end exponent straight y space plus space 1 half left parenthesis 1 plus space log space straight x right parenthesis squared space plus space straight c space equals space 0
    which is the required solution. 

    Question 224
    CBSEENMA12033055

    Solve:
     left parenthesis 1 plus straight e to the power of 2 straight x end exponent right parenthesis space dy space plus space left parenthesis 1 plus straight y squared right parenthesis space straight e to the power of straight x space dx space equals space 0

    Solution
    The given differential equation is
          left parenthesis 1 plus straight e to the power of 2 straight x end exponent right parenthesis space dy space plus space left parenthesis 1 plus straight y squared right parenthesis space straight e to the power of straight x space dx space equals space 0 space space or space space left parenthesis 1 plus straight e to the power of 2 straight x end exponent right parenthesis space dy space equals space minus left parenthesis 1 plus straight y squared right parenthesis space straight e to the power of straight x space dx
    Separating the variables, we get,
                     fraction numerator 1 over denominator 1 plus straight y squared end fraction dy space equals space minus fraction numerator straight e to the power of straight x over denominator 1 plus straight e to the power of 2 straight x end exponent end fraction dx
    Integrating, integral fraction numerator 1 over denominator 1 plus straight y squared end fraction dy space equals space minus integral fraction numerator straight e to the power of straight x over denominator 1 plus straight e to the power of 2 straight x end exponent end fraction dx             ...(1)
    Let          straight I space equals integral fraction numerator straight e to the power of straight x over denominator 1 plus straight e to the power of 2 straight x end exponent end fraction dx
    Put straight e to the power of straight x space equals space straight t comma space space space space therefore space space space straight e to the power of straight x dx space equals space dt
    therefore space space space space space space space space space straight I space equals space integral fraction numerator 1 over denominator 1 plus straight t squared end fraction dt space space equals space tan to the power of negative 1 end exponent straight t plus straight c subscript 1 space equals space tan to the power of negative 1 end exponent left parenthesis straight e to the power of straight x right parenthesis space plus space straight c subscript 1
therefore space space space space from space left parenthesis 1 right parenthesis comma space space space tan to the power of negative 1 end exponent straight y space equals space minus tan to the power of negative 1 end exponent left parenthesis straight e to the power of straight x right parenthesis space plus space straight c subscript 1
therefore space space space space tan to the power of negative 1 end exponent straight y space plus space tan to the power of negative 1 end exponent left parenthesis straight e to the power of straight x right parenthesis space equals space straight c subscript 1
therefore space space space tan to the power of negative 1 end exponent open parentheses fraction numerator straight y plus straight e to the power of straight x over denominator 1 minus ye to the power of straight x end fraction close parentheses space equals space straight c subscript 1
therefore space space space fraction numerator straight y plus straight e to the power of straight x over denominator 1 minus ye to the power of straight x end fraction space equals space straight c comma space space space where space straight c space equals space tan space straight c subscript 1
    This is the required solution. 
    Question 225
    CBSEENMA12033056

    Solve:
    log dy over dx equals ax plus by.
     

    Solution
    The given differential equation is
                 log space dy over dx space equals space ax plus by space space space space or space space space space dy over dx space equals space straight e to the power of ax plus by end exponent
    or          dy over dx space equals space straight e to the power of ax. space straight e to the power of by.
    Separating the variables, we get, 
                    1 over straight e to the power of by dy space equals space straight e to the power of ax dx
    Integrating,     integral straight e to the power of negative by end exponent dy space equals space straight e to the power of ax dx
    therefore space space space space space space fraction numerator straight e to the power of negative by end exponent over denominator negative straight b end fraction space equals space straight e to the power of ax over straight a plus straight c space space space space space or space space space space minus 1 over straight b straight e to the power of negative by end exponent space equals space 1 over straight a straight e to the power of ax plus straight c
    which is required solution. 
    Question 226
    CBSEENMA12033057

    Solve:
    straight x squared left parenthesis straight y minus 1 right parenthesis space dx space plus space straight y squared space left parenthesis straight x minus 1 right parenthesis space dy space equals space 0

     

    Solution

    The given differential equation is
                 straight x squared left parenthesis straight y minus 1 right parenthesis space dx space plus space straight y squared left parenthesis straight x minus 1 right parenthesis space dy space equals space 0 space space or space space straight y squared left parenthesis straight x minus 1 right parenthesis space dy space equals space minus straight x squared left parenthesis straight y minus 1 right parenthesis space dx
    or      fraction numerator straight y squared over denominator straight y minus 1 end fraction dy space equals space minus fraction numerator straight x squared over denominator straight x minus 1 end fraction dx
    Integrating,   integral fraction numerator straight y squared over denominator straight y minus 1 end fraction dy space equals space minus integral fraction numerator straight x squared over denominator straight x minus 1 end fraction dx
    therefore space space space space space integral open parentheses straight y plus 1 plus fraction numerator 1 over denominator straight y minus 1 end fraction close parentheses dy space equals space minus integral open parentheses straight x plus 1 plus fraction numerator 1 over denominator straight x minus 1 end fraction close parentheses dx
therefore space space straight y squared over 2 plus straight y plus log space open vertical bar straight y minus 1 close vertical bar space equals space minus open square brackets straight x squared over 2 plus straight x plus log space open vertical bar straight x plus 1 close vertical bar close square brackets plus straight c
    is the required solution. 

    Question 227
    CBSEENMA12033058

    Solve:
    open parentheses straight e to the power of straight x plus 1 close parentheses space straight y space dy space plus space left parenthesis straight y plus 1 right parenthesis space straight e to the power of straight x space dx space equals space 0


     

    Solution
    The given differential equation is
                          open parentheses straight e to the power of straight x plus 1 close parentheses space straight y space dy space plus space left parenthesis straight y plus 1 right parenthesis space straight e to the power of straight x space dx space equals space 0
    or                open parentheses straight e to the power of straight x plus 1 close parentheses straight y space dy space equals space minus left parenthesis straight y plus 1 right parenthesis space straight e to the power of straight x dx
    or                fraction numerator straight y over denominator straight y plus 1 end fraction dy space equals space minus fraction numerator straight e to the power of straight x over denominator straight e to the power of straight x plus 1 end fraction dx
    Integrating,   integral fraction numerator straight y over denominator straight y plus 1 end fraction dy space equals space minus integral fraction numerator straight e to the power of straight x over denominator straight e to the power of straight x plus 1 end fraction dx
    therefore space space space space integral open parentheses 1 minus fraction numerator 1 over denominator straight y plus 1 end fraction close parentheses space dy space equals space minus integral fraction numerator straight e to the power of straight x over denominator straight e to the power of straight x plus 1 end fraction dx
therefore space space straight y minus log space open vertical bar straight y plus 1 close vertical bar space equals space minus space log space left parenthesis straight e to the power of straight x plus 1 right parenthesis space plus straight c
    which is the required solution. 
    Question 228
    CBSEENMA12033059

    Solve:
    straight y left parenthesis 1 minus straight x squared right parenthesis space dy space plus space straight x space left parenthesis 1 plus straight y squared right parenthesis space dx space equals space 0.



     

    Solution
    The given differential equation is
                   straight y left parenthesis 1 minus straight x squared right parenthesis space dy space plus space straight x space left parenthesis 1 plus straight y squared right parenthesis space dx space equals space 0
    or          straight y left parenthesis 1 minus straight x squared right parenthesis space dy space equals space minus straight x left parenthesis 1 plus straight y squared right parenthesis space dx
    or           fraction numerator straight y over denominator 1 plus straight y squared end fraction dy space equals space minus fraction numerator straight x over denominator 1 minus straight x squared end fraction dx
    Integrating,   integral fraction numerator straight y over denominator 1 plus straight y squared end fraction dy equals space space minus integral fraction numerator straight x over denominator 1 minus straight x squared end fraction dx
    therefore space space space space integral fraction numerator 2 straight y over denominator 1 plus straight y squared end fraction dy space equals space integral space fraction numerator negative 2 straight x over denominator 1 minus straight x squared end fraction dx
therefore space space log space left parenthesis 1 plus straight y squared right parenthesis space equals space log space open vertical bar 1 minus straight x squared close vertical bar plus straight c
    which is required solution. 
    Question 229
    CBSEENMA12033060

    Solve:
    straight y space logydx space minus space straight x space dy space equals space 0



     

    Solution
    The given differential equation is
      y log y dx - x dy = 0    or   y log y dx =  x dy
    or          fraction numerator 1 over denominator straight y space log space straight y end fraction dy space equals space 1 over straight x dx
    Integrating,     integral fraction numerator begin display style 1 over straight y end style over denominator log space straight y end fraction dy space equals space integral 1 over straight x dx
    therefore space space space space space space space space log space open vertical bar log space straight y close vertical bar space equals space log space open vertical bar straight x close vertical bar space plus space log space straight A
therefore space space space space space space space space log space open vertical bar log space straight y close vertical bar space minus space log space open vertical bar straight x close vertical bar space equals space log space straight A
therefore space space space space log space open parentheses fraction numerator open vertical bar log space straight y close vertical bar over denominator open vertical bar straight x close vertical bar end fraction close parentheses space equals space log space straight A
therefore space space space space space space space space space space space space open vertical bar fraction numerator log space straight y over denominator straight x end fraction close vertical bar space equals space straight A space space or space space space space fraction numerator log space straight y over denominator straight x end fraction space equals space plus-or-minus space straight A
therefore space space space space space space space space fraction numerator log space straight y over denominator straight x end fraction space equals space straight c comma space space space where space straight c space equals space plus-or-minus straight A
or space space space space space space space log space straight y space equals space straight c space straight x space space space space space space space rightwards double arrow space space space space straight y space equals space straight e to the power of cx space is space required space solution.
    Question 230
    CBSEENMA12033061

    Show that the general solution of the differential equation dy over dx plus fraction numerator straight y squared plus straight y plus 1 over denominator straight x squared plus straight x plus 1 end fraction space equals 0 is given by (x + y + 1) = A (1 – x – y – 2 x y), where A is parameter.

    Solution

    The given differential equation is
                          dy over dx plus fraction numerator straight y squared plus straight y plus 1 over denominator straight x squared plus straight x plus 1 end fraction space equals space 0 space or space space fraction numerator dy over denominator straight y squared plus straight y plus 1 end fraction plus fraction numerator dx over denominator straight x squared plus straight x plus 1 end fraction space equals space 1
    Integrating, we get
                             integral fraction numerator dy over denominator straight y squared plus straight y plus 1 end fraction plus integral fraction numerator dx over denominator straight x squared plus straight x plus 1 end fraction space equals space straight C
    rightwards double arrow space space space space space integral space fraction numerator dy over denominator open parentheses straight y plus begin display style 1 half end style close parentheses squared plus open parentheses 1 minus begin display style 1 fourth end style close parentheses end fraction plus integral fraction numerator dx over denominator open parentheses straight x plus begin display style 1 half end style close parentheses squared plus 1 minus begin display style 1 fourth end style end fraction space equals space straight C
rightwards double arrow space space space space integral space fraction numerator dy over denominator open parentheses straight y plus begin display style 1 half end style close parentheses squared plus open parentheses begin display style fraction numerator square root of 3 over denominator 2 end fraction end style close parentheses squared end fraction plus integral fraction numerator dx over denominator open parentheses straight x plus begin display style 1 half end style close parentheses squared plus open parentheses begin display style fraction numerator square root of 3 over denominator 2 end fraction end style close parentheses squared end fraction space equals space straight C
rightwards double arrow space space space space fraction numerator 2 over denominator square root of 3 end fraction tan to the power of negative 1 end exponent open parentheses fraction numerator straight y plus begin display style 1 half end style over denominator begin display style fraction numerator square root of 3 over denominator 2 end fraction end style end fraction close parentheses plus fraction numerator 2 over denominator square root of 3 end fraction tan to the power of negative 1 end exponent open parentheses fraction numerator straight x plus begin display style 1 half end style over denominator begin display style fraction numerator square root of 3 over denominator 2 end fraction end style end fraction close parentheses space equals space straight C
rightwards double arrow space space tan to the power of negative 1 end exponent open parentheses fraction numerator 2 straight y plus 1 over denominator square root of 3 end fraction close parentheses space plus space tan to the power of negative 1 end exponent space open parentheses fraction numerator 2 straight x plus 1 over denominator square root of 3 end fraction close parentheses space equals space fraction numerator square root of 3 straight C over denominator 2 end fraction space equals space straight A subscript 1 space left parenthesis say right parenthesis
    Taking tangents on the two sides, we get
                         fraction numerator begin display style fraction numerator 2 straight y plus 1 over denominator square root of 3 end fraction end style plus begin display style fraction numerator 2 straight x plus 1 over denominator square root of 3 end fraction end style over denominator 1 minus open parentheses begin display style fraction numerator 2 straight y plus 1 over denominator square root of 3 end fraction end style close parentheses space open parentheses begin display style fraction numerator 2 straight x plus 1 over denominator square root of 3 end fraction end style close parentheses end fraction space equals space tan space straight A subscript 1 space space rightwards double arrow space space space fraction numerator 2 square root of 3 space left parenthesis straight x plus straight y plus 1 right parenthesis over denominator 3 minus left parenthesis 4 space straight x space straight y space plus 2 straight x plus 2 straight y plus 1 right parenthesis end fraction equals space tan space straight A subscript 1
    rightwards double arrow space space space space space space fraction numerator 2 square root of 3 left parenthesis straight x plus straight y plus 1 right parenthesis over denominator 2 left parenthesis 1 minus straight x minus straight y minus 2 xy right parenthesis end fraction space equals space tan space straight A subscript 1
rightwards double arrow space space space space straight x plus straight y plus 1 space equals space fraction numerator 1 over denominator square root of 3 end fraction tan space straight A subscript 1 space left parenthesis 1 minus straight x minus straight y minus 2 xy right parenthesis
rightwards double arrow space space space straight x plus straight y plus 1 space equals space straight A left parenthesis 1 minus straight x minus straight y minus 2 xy right parenthesis comma
                 where straight A space equals space fraction numerator 1 over denominator square root of 3 end fraction space space tan space straight A subscript 1 space is space an space arbitrary space constant. space

    Question 231
    CBSEENMA12033062

    Solve:
    dy over dx space equals space fraction numerator straight x left parenthesis 2 space log space straight x space plus space 1 right parenthesis over denominator sin space straight y space plus space straight y space cosy end fraction

    Solution

    The given differential equation is
                dy over dx space equals space fraction numerator straight x left parenthesis 2 space log space straight x space plus space 1 right parenthesis over denominator sin space straight y space plus space straight y space cosy end fraction
    Separating the variables, we get,
                                       left parenthesis sin space straight y space plus space straight y space cosy right parenthesis space dy space equals space straight x left parenthesis 2 space logx space plus 1 right parenthesis space dx
    therefore space space space space integral left parenthesis sin space straight y space plus straight y space cos right parenthesis space dy space equals space integral straight x space left parenthesis 2 space log space straight x space plus 1 right parenthesis space dx
therefore space space space integral sin space ydy space plus space integral straight y space cosy space dy space equals space 2 space integral logx. space straight x space dx space plus space integral straight x space dx
therefore space space space space space space space minus cosy space plus space straight y space siny space minus space integral 1. space sin space straight y space dy space equals space 2 open square brackets left parenthesis log space straight x right parenthesis. space straight x squared over 2 minus integral 1 over straight x. straight x squared over 2 dx plus straight x squared over 2 close square brackets
therefore space space space minus cosy space plus space ysiny space space plus space cosy space space equals space straight x squared logx minus straight x squared over 2 plus straight x squared over 2 plus straight c
therefore space space space straight y space sin space straight y space equals space straight x squared space logx space plus straight c space which space is space required space equation.

    Question 232
    CBSEENMA12033063

    Solve
    dy over dx space equals space fraction numerator xe to the power of straight x logx plus straight e to the power of straight x over denominator straight x space cosy end fraction

    Solution

    The given differential equation is dy over dx equals fraction numerator xe to the power of straight x logx plus straight e to the power of straight x over denominator straight x space cosy end fraction
    Separating the variables, we get,
                cosy space dy space equals space fraction numerator xe to the power of straight x logx plus straight e to the power of straight x over denominator straight x end fraction dx space space or space space cosy space dy space equals space straight e to the power of straight x open parentheses fraction numerator straight x space logx space plus space 1 over denominator straight x end fraction close parentheses dx
    or     cosy space dy space equals space straight e to the power of straight x open parentheses logx plus 1 over straight x close parentheses dx space space space rightwards double arrow space space integral space cosy space dy space equals space integral straight e to the power of straight x open parentheses logx plus 1 over straight x close parentheses dx
    therefore space space space sin space straight y space equals space straight e to the power of straight x space logx space plus space straight c space space space space space space space space space open square brackets because space space integral straight e to the power of straight x open curly brackets straight f left parenthesis straight x right parenthesis plus straight f apostrophe left parenthesis straight x right parenthesis close curly brackets dx space equals space straight e to the power of straight x space straight f left parenthesis straight x right parenthesis space plus space straight c close square brackets
    which is required solution. 

    Question 233
    CBSEENMA12033064

    Solve
    dy over dx space equals space sin cubed straight x space cos squared straight x plus straight x space straight e to the power of straight x

    Solution

    The given differential equation is
                  dy over dx space equals space sin cubed straight x space cos squared straight x plus straight x space straight e to the power of straight x
    Separting the variables, we get,   dy space equals space left parenthesis sin cubed straight x space cos squared straight x plus straight x space straight e to the power of straight x right parenthesis space dx
    therefore space space space space integral dy space equals space integral left parenthesis sin cubed straight x space cos squared straight x plus straight x space straight e to the power of straight x right parenthesis space dx
therefore space space integral dy space equals space integral sin cubed straight x space cos squared straight x space dx space plus space integral straight x space straight e to the power of straight x space dx space space space space space space... space left parenthesis 1 right parenthesis
    Let   straight I subscript 1 space equals space integral sin cubed straight x space space cos squared straight x space dx space equals space integral sin squared straight x space cos squared straight x. space sinx space dx
                equals space integral left parenthesis 1 minus cos squared straight x right parenthesis space cos squared straight x. space sinx space dx
    Put cosx =t,     therefore space space space space sin space straight x space dx space equals space minus dt
    therefore space space space straight I subscript 1 space equals space minus integral left parenthesis 1 minus straight t squared right parenthesis space straight t squared space dt space equals space minus integral left parenthesis straight t squared minus straight t to the power of 4 right parenthesis space dt space equals space minus open parentheses straight t cubed over 3 minus straight t to the power of 5 over 5 close parentheses equals 1 fifth straight t to the power of 5 minus 1 third straight t cubed
                 equals space 1 fifth cos to the power of 5 straight x space minus space 1 third cos cubed straight x
    Let   straight I subscript 2 space equals space integral straight x space straight e to the power of straight x space dx space equals space straight x space. straight e to the power of straight x space minus space integral 1. space straight e to the power of straight x space dx space equals space straight x space straight e to the power of straight x space minus space straight e to the power of straight x space equals space left parenthesis straight x minus 1 right parenthesis space straight e to the power of straight x
    therefore space space space from space left parenthesis 1 right parenthesis comma space space integral dy space equals space 1 fifth cos to the power of 5 straight x minus 1 third cos cubed straight x plus left parenthesis straight x minus 1 right parenthesis space straight e to the power of straight x
therefore space space space straight y space equals space 1 fifth cos to the power of 5 straight x space minus space 1 third cos cubed straight x space plus space left parenthesis straight x minus 1 right parenthesis space straight e to the power of straight x plus straight c space is space the space required space solution. space      

    Question 234
    CBSEENMA12033065

    Solve:
    dy over dx space equals space cos cubed straight x space sin to the power of 4 straight x plus straight x square root of 2 straight x plus 1 end root


    Solution
    The given differential equation is  dy over dx space equals space cos cubed straight x space sin to the power of 4 straight x plus straight x square root of 2 straight x plus 1 end root
    Separating the variables, we get,   dy space equals space left parenthesis cos cubed straight x space sin to the power of 4 straight x plus straight x square root of 2 straight x plus 1 end root right parenthesis space dx
    therefore space space space integral dy space equals space integral left parenthesis cos cubed straight x space sin to the power of 4 straight x plus straight x square root of 2 straight x plus 1 end root right parenthesis space dx
    or space space space integral dy space equals space integral cos cubed straight x space sin to the power of 4 straight x space dx plus integral straight x space square root of 2 straight x plus 1 end root space dx                ...(1)
    Let I = integral space cos cubed straight x space sin to the power of 4 straight x space dx space equals space integral cos squared straight x. space sin to the power of 4 straight x. space cosx space dx
            equals space integral left parenthesis 1 minus sin squared straight x right parenthesis space sin to the power of 4 straight x. space cosx space dx
    Put sin space straight x space equals space straight t comma space space space therefore space space cos space straight x space dx space equals space dt
    therefore space space space straight I space equals space integral left parenthesis 1 minus straight t squared right parenthesis space straight t to the power of 4 space dt space equals space integral left parenthesis straight t to the power of 4 minus straight t to the power of 6 right parenthesis space dt space equals space 1 fifth space straight t to the power of 5 space minus space 1 over 7 straight t to the power of 7 space equals 1 fifth sin to the power of 5 straight x minus 1 over 7 sin to the power of 7 straight x
    Let straight I subscript 1 space equals space integral straight x square root of 2 straight x plus 1 end root space dx
    Put square root of 2 straight x plus 1 end root space equals space straight y comma space space space space space therefore space space 2 straight x plus 1 space equals space straight y squared space space rightwards double arrow space space space 2 straight x space equals space straight y squared minus 1 space space rightwards double arrow space straight x space equals space 1 half left parenthesis straight y squared minus 1 right parenthesis
    therefore space space space space dx space equals space 1 half space 2 straight y space dy space equals space straight y space dy
therefore space space space straight I subscript 1 space equals space integral fraction numerator straight y squared minus 1 over denominator 2 end fraction. straight y. space straight y space dy space equals space 1 half integral left parenthesis straight y squared minus 1 right parenthesis space straight y squared space dy space equals space 1 half integral left parenthesis straight y to the power of 4 minus straight y squared right parenthesis space dy space equals 1 half open square brackets straight y to the power of 5 over 5 minus straight y cubed over 3 close square brackets
space space space space space space space space space space space space equals space 1 over 10 straight y to the power of 5 space minus space 1 over 6 straight y cubed space equals space 1 over 10 left parenthesis 2 straight x plus 1 right parenthesis to the power of 5 divided by 2 end exponent minus space 1 over 6 left parenthesis 2 straight x plus 1 right parenthesis to the power of 3 divided by 2 end exponent
    therefore space space space space from space left parenthesis 1 right parenthesis comma space we space get comma space
space space space space space space space space space space integral dy space equals space 1 fifth sin to the power of 5 straight x minus 1 over 7 sin to the power of 7 straight x plus 1 over 10 left parenthesis 2 straight x plus 1 right parenthesis to the power of 5 divided by 2 end exponent minus 1 over 6 left parenthesis 2 straight x plus 1 right parenthesis to the power of 3 divided by 2 end exponent
therefore space space space space straight y space equals space 1 fifth sin to the power of 5 straight x minus 1 over 7 sin to the power of 7 straight x plus 1 over 10 left parenthesis 2 straight x plus 1 right parenthesis to the power of 5 divided by 2 end exponent minus 1 over 6 left parenthesis 2 straight x plus 1 right parenthesis to the power of 3 divided by 2 end exponent plus straight c
    Question 235
    CBSEENMA12033066

    Solve:
    dy over dx equals negative straight x space sin squared straight x space space equals space fraction numerator 1 over denominator straight x space log space straight x end fraction



    Solution
    dy over dx minus straight x space sin squared straight x space equals space fraction numerator 1 over denominator straight x space log space straight x end fraction space or space dy over dx space equals straight x space sin squared straight x space plus space fraction numerator 1 over denominator straight x space logx end fraction
    Separating the variables, we get, 
        dy equals open parentheses straight x space sin squared straight x plus fraction numerator 1 over denominator straight x space logx space end fraction close parentheses dx space space space space rightwards double arrow space space integral dy space equals space integral open parentheses xsin squared straight x plus fraction numerator 1 over denominator straight x space logx end fraction close parentheses dx
    therefore space space space integral space dy space equals integral straight x space sin squared straight x space dx plus integral fraction numerator 1 over denominator straight x space logx space dx end fraction
therefore space space space integral dy space equals space straight I subscript 1 plus straight I subscript 2 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
    where   straight I subscript 1 space equals space integral straight x space sin squared space dx space equals space 1 half integral straight x space left parenthesis 2 space sin squared straight x right parenthesis space dx
                        equals space 1 half integral straight x left parenthesis 1 minus cos space 2 straight x right parenthesis space dx space equals space 1 half integral straight x space dx space minus space 1 half integral straight x. space cos space 2 straight x space dx
                        equals space straight x squared over 4 minus 1 fourth straight x space sin space 2 straight x space plus space 1 fourth integral sin space 2 straight x space dx space equals space straight x squared over 4 minus 1 fourth straight x space sin 2 straight x space minus 1 over 8 cos space 2 straight x
                  straight I subscript 2 space equals integral fraction numerator 1 over denominator straight x space logx end fraction dx space equals space integral fraction numerator begin display style 1 over straight x end style over denominator log space straight x end fraction dx space equals space log space open vertical bar log space straight x close vertical bar
    therefore space space space from space left parenthesis 1 right parenthesis comma space we space get,
                       integral dy space equals space straight x squared over 4 minus 1 fourth straight x space sin space 2 straight x space minus 1 over 8 cos space 2 straight x space plus space log space open vertical bar log space straight x close vertical bar
    therefore space space space straight y space equals space straight x squared over 4 minus 1 fourth straight x space sin space 2 straight x space minus space 1 over 8 cos space 2 straight x space plus space log space open vertical bar logx close vertical bar space plus straight c which is the required solution.
    Question 236
    CBSEENMA12033067

    Show that the given differential equation is homogeneous and solve it.
    (x2 – y2) dx + 2xy dy = 0
    given that y = 1 when x = 1.

    Solution
    The given differential equation is
        open parentheses straight x squared minus straight y squared close parentheses space dx space plus space 2 xy space dy space equals space 0 space space space space or space space space 2 xy space dy space equals space left parenthesis straight y squared minus straight x squared right parenthesis space dx
    or             dy over dx space equals space fraction numerator straight y squared minus straight x squared over denominator 2 xy end fraction
    Put y = vx so that dy over dx equals space straight v plus straight x dv over dx
    therefore space space space space straight v plus straight x dv over dx equals fraction numerator straight v squared straight x squared minus straight x squared over denominator 2 vx squared end fraction space space space or space space space straight v plus straight x dv over dx space equals space fraction numerator straight v squared minus 1 over denominator 2 space straight v end fraction
    therefore space space space space space space space space space space space straight x dv over dx equals fraction numerator straight v squared minus 1 over denominator 2 space straight v end fraction minus straight v space space space or space space space straight x dv over dx space equals space fraction numerator straight v squared minus 1 minus 2 straight v squared over denominator 2 straight v end fraction
therefore space space space space space space space space straight x dv over dx space equals space fraction numerator negative 1 minus straight v squared over denominator 2 space straight v end fraction space space space space space rightwards double arrow space space space space space space space fraction numerator 2 space straight v over denominator 1 plus straight v squared end fraction dv space equals space minus 1 over straight x dx
therefore space space space space space space integral fraction numerator 2 space straight v over denominator 1 plus straight v squared end fraction dv space equals space minus integral 1 over straight x dx
therefore space space space log space open vertical bar 1 plus straight v squared close vertical bar space equals space minus log space open vertical bar straight x close vertical bar plus straight c apostrophe
therefore space space space log space open vertical bar 1 plus straight v squared close vertical bar plus log space open vertical bar straight x close vertical bar space equals space straight c apostrophe
therefore space log space open vertical bar left parenthesis 1 plus straight v squared right parenthesis space left parenthesis straight x right parenthesis close vertical bar space equals space straight c apostrophe
therefore space space space space space space straight x left parenthesis 1 plus straight v squared right parenthesis space equals space straight c apostrophe space space space space space space space rightwards double arrow space space space space space straight x space open parentheses 1 plus straight y squared over straight x squared close parentheses space equals space straight c
therefore space space space space space space straight x squared plus straight y squared space equals space straight c space straight x
    Now,  straight y space equals space 1 comma space space when space straight x space equals space 1
    therefore space space space space space space space space space space 1 plus 1 space equals space straight c space space space space space space space space space space space space space space space space space space space space space rightwards double arrow space space space straight c space equals space 2
therefore space space space solution space is space straight x squared plus straight y squared space equals space 2 straight x.
    Question 237
    CBSEENMA12033068

    Solve the differential equation:
    dy over dx space equals space straight y space sin space 2 straight x comma space space space given space that space space straight y left parenthesis 0 right parenthesis space equals space 1.

    Solution
    The given differential equation is
                               dy over dx space equals space straight y space sin space 2 straight x
    Separating the variables, we get,
                        1 over straight y dy space equals space sin space 2 straight x space dx
    Integrating,  integral 1 over straight y dy space equals space integral sin space 2 straight x space dx
    therefore space space space log space open vertical bar straight y close vertical bar space equals space minus fraction numerator cos space 2 straight x over denominator 2 end fraction plus straight c                          ...(1)
    Now     straight y left parenthesis 0 right parenthesis space equals space 1 space space space space space space space space space space space space rightwards double arrow space space space straight y space equals space 1 space space space space when space straight x space equals space 0
    therefore space space log space open vertical bar 1 close vertical bar space equals space minus fraction numerator cos space 0 over denominator 2 end fraction plus straight c space space space space space rightwards double arrow space space 0 space equals space minus 1 half plus straight c space space space space rightwards double arrow space space space space straight c space equals space 1 half
therefore space space from space left parenthesis 1 right parenthesis space space space log space open vertical bar straight y close vertical bar space equals space minus 1 half space cos space 2 straight x space plus 1 half space which space is space required space solution. space
    Question 238
    CBSEENMA12033069

    Solve the following initial value problem:
    (1 + x y) y dx + (1 – x y) x dy = 0, y (1) = 1.

    Solution
    The given differential equation is
                        (1 + x y) y dx + (1 – x y) x dy = 0
    or            left parenthesis straight y space dx space plus space straight x space dy right parenthesis space plus space straight x space straight y squared space dx space minus space straight x squared straight y space dy space equals space 0
    or            fraction numerator ydx plus xdy over denominator straight x squared straight y squared end fraction plus 1 over straight x dx minus 1 over straight y dy space equals space 0
    therefore space space space space space integral fraction numerator straight y space dx space plus space straight x space dy over denominator straight x squared straight y squared end fraction plus integral 1 over straight x dx space minus space integral 1 over straight y dy space equals space 0               ...(1)
    Let I = integral fraction numerator straight y space dx space plus space straight x space dy over denominator straight x squared straight y squared end fraction
    Put x y  = t so that  x dy + y dx = dt
    therefore space space space space straight I space equals space integral 1 over straight t squared dt space equals space integral straight t to the power of negative 2 end exponent dt space equals space fraction numerator straight t to the power of negative 1 end exponent over denominator negative 1 end fraction space equals space minus 1 over straight t space equals negative fraction numerator 1 over denominator straight x space straight y end fraction
    therefore  from (1),
            negative 1 over xy plus logx minus logy space equals space straight c                             
    Now     straight y left parenthesis 1 right parenthesis space equals space 1 space space space space space space space space space space space space space space space rightwards double arrow space space space space straight y space equals 1 space space space space when space straight x space equals space 1
    therefore space space space minus 1 over 1 plus log space 1 space minus space log space 1 space equals space straight c space space space rightwards double arrow space space space space straight c space equals space minus 1
    therefore space space space space from space left parenthesis 1 right parenthesis comma space solution space of space differential space equation space is space
space space space space space space space space space minus 1 over xy plus log space straight x space minus space log space straight y space equals space minus 1
therefore space space space log space straight x space equals space log space straight y space plus space fraction numerator 1 over denominator straight x space straight y end fraction minus 1
    which is required solution. 
    Question 239
    CBSEENMA12033070

    Find the particular solution of the differential equation dy over dx space equals space minus 4 xy squared given that y = 1,  when x = 0.

    Solution
    The given differential equation is
                                             dy over dx equals negative 4 space straight x space straight y squared
    Separating the variables, we get,
                         1 over straight y squared dy space equals space minus 4 straight x space dx
    Integrating,   integral 1 over straight y squared dy space equals space minus 4 integral space straight x space dx space space or space space space integral space straight y to the power of negative 2 end exponent space dy space equals space minus 4 space integral space straight x space dx
    therefore space space space space space space space space space space space space fraction numerator straight y to the power of negative 1 end exponent over denominator negative 1 end fraction space equals negative 4 straight x squared over 2 plus straight c
or space space space space space space space space space space space space space space space space fraction numerator negative 1 over denominator straight y end fraction space equals space minus 2 straight x squared plus straight c space space or space space space 1 over straight y space equals space 2 straight x squared minus straight c
or space space space space space space space space space space space space space space space space straight y space equals space fraction numerator 1 over denominator 2 straight x squared minus straight c end fraction space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
    Now y = 1 when x = 0
    therefore space space space space space space space space space space space space space space space space space space space space space space 1 space equals space fraction numerator 1 over denominator 0 minus straight c end fraction space space or space space space 1 space equals space 1 over straight c space space rightwards double arrow space space straight c space equals space 1
    Putting c = -1 in (1), we get,
                                              straight y space equals fraction numerator 1 over denominator 2 straight x squared plus 1 end fraction comma space which space is space required space solution. space
    Question 240
    CBSEENMA12033071

    Find the particular solution of the differential equation
    (1 + e2x ) dy + (1 + y2 ) ex dx = 0, given that y = 1 when x = 0.

    Solution

    The given differential equation is
                  (1 + e2x ) dy + (1 + y2 ) ex dx = 0   or   (1 + e2x ) dy  = - (1 + y2 ) ex dx
    therefore space space space space fraction numerator 1 over denominator 1 plus straight y squared end fraction dy space equals negative space fraction numerator straight e to the power of straight x over denominator 1 plus straight e to the power of 2 straight x end exponent end fraction dx
    rightwards double arrow space space space space integral fraction numerator 1 over denominator 1 plus straight y squared end fraction dy space equals space minus integral fraction numerator straight e to the power of straight x over denominator 1 plus straight e to the power of 2 straight x end exponent end fraction dx space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
    Let I = integral fraction numerator straight e to the power of straight x over denominator 1 plus straight e to the power of 2 straight x end exponent end fraction dx
    Put         straight e to the power of straight x space equals space straight t comma space space space therefore space space space space straight e to the power of straight x space dx space equals space dt
    therefore space space space space straight I space equals space integral fraction numerator dt over denominator 1 plus straight t squared end fraction space equals space tan to the power of negative 1 end exponent straight t space equals space tan to the power of negative 1 end exponent left parenthesis straight e to the power of straight x right parenthesis
therefore space space space space from space left parenthesis 2 right parenthesis comma space space tan to the power of negative 1 end exponent straight y space equals space tan left parenthesis straight e to the power of straight x right parenthesis space plus straight c space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis
    Now,   x = 0,  y = 1
    therefore space space space tan to the power of negative 1 end exponent 1 space equals space minus tan left parenthesis straight e to the power of 0 right parenthesis space plus space straight c space space space rightwards double arrow space space space space straight pi over 4 space equals space minus tan to the power of negative 1 end exponent left parenthesis 1 right parenthesis space plus space straight c
rightwards double arrow space space space straight pi over 4 space equals space minus straight pi over 4 plus straight c space space space rightwards double arrow space space space space straight c space equals space straight pi over 2
therefore space space from space left parenthesis 2 right parenthesis comma space tan to the power of negative 1 end exponent straight y equals space minus tan space straight e to the power of straight x plus straight pi over 2 comma space which space is space required space solution. space

    Question 241
    CBSEENMA12033072

    Find the solution of the equation:
                dy over dx space equals space straight e to the power of straight x plus straight y end exponent plus straight x squared space straight e to the power of straight x
    subject to the condition, when x = 0;  y = 0.

    Solution
    dy over dx space equals space straight e to the power of straight x plus straight y end exponent plus straight x squared straight e to the power of straight x space space space space space space rightwards double arrow space space space dy over dx space equals space straight e to the power of straight x. space straight e to the power of straight y space plus space straight x squared space straight e to the power of straight x space space rightwards double arrow space space dy over dx space equals space left parenthesis straight e to the power of straight x plus straight x squared right parenthesis space straight e to the power of straight y
    Separating the variables, we get,  dy over straight e to the power of straight y space equals space left parenthesis straight e to the power of straight x plus straight x squared right parenthesis space dx
    therefore space space space space space space space integral straight e to the power of negative straight y end exponent dy space equals space integral left parenthesis straight e to the power of straight x plus straight x squared right parenthesis space dx space space space space space rightwards double arrow space space space fraction numerator straight e to the power of negative straight y end exponent over denominator negative 1 end fraction space equals space straight e to the power of straight x plus straight x cubed over 3 plus straight c
    or             straight e to the power of negative straight y end exponent plus straight e to the power of straight x plus straight x cubed over 3 plus straight c space equals space 0                       ...(1)
    When x = 0,  y = 0,  we have
                    straight e to the power of 0 plus straight e to the power of 0 plus 0 plus straight c space equals space 0 space space space space rightwards double arrow space space space space 1 plus 1 plus straight c space equals space 0 space space space rightwards double arrow space space space straight c space equals negative space 2
    Putting c = -2 in (1), the required solution is
                         e to the power of italic minus x end exponent italic plus e to the power of x italic plus x to the power of italic 3 over italic 3 italic minus italic 2 italic space italic equals italic space italic 0 italic.
    Question 242
    CBSEENMA12033073

    Solve the differential equation;
    x (1 + y2 ) dx – y (1 + x2 ) dy = 0  given that y = 0 when x = 1. 

    Solution
    The given differential equation is
               x (1 + y2 ) dx – y (1 + x2 ) dy = 0 
    or              y (1 + x2 ) dy = 0 =    x (1 + y2 ) dx
    therefore space space space space space space space space space space space space fraction numerator straight y over denominator 1 plus straight y squared end fraction dy space equals space fraction numerator straight x over denominator 1 plus straight x squared end fraction dx
rightwards double arrow space space space space space space space space space space fraction numerator 2 straight y over denominator 1 plus straight y squared end fraction dy space equals space fraction numerator 2 straight x over denominator 1 plus straight x squared end fraction dx
    Integrating, integral fraction numerator 2 straight y over denominator 1 plus straight y squared end fraction dy space equals space integral fraction numerator 2 straight x over denominator 1 plus straight x squared end fraction dx
    therefore space space space space space space space space space space space space space log space left parenthesis 1 plus straight y squared right parenthesis space equals space log space left parenthesis 1 plus straight x squared right parenthesis space plus space log space straight c
therefore space space space space space space space space log space left parenthesis 1 plus straight y squared right parenthesis space equals space log space left square bracket straight c space left parenthesis 1 plus straight x squared right parenthesis right square bracket
rightwards double arrow space space space space space space space space space space space space space space space space space space space space space space space space 1 plus straight y squared space equals space straight c space left parenthesis 1 plus straight x squared right parenthesis space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
    Now   y = 0 when x = 1
    therefore space space space space space space space space space 1 plus 0 space equals space straight c space left parenthesis 1 plus 1 right parenthesis space space or space space space space 1 space equals space 2 straight c space space space space rightwards double arrow space space straight c space equals space 1 half
therefore space space space space from space left parenthesis 1 right parenthesis comma space space space space space space space 1 plus straight y squared space equals space 1 half left parenthesis 1 plus straight x squared right parenthesis
    which is required solution. 
    Question 243
    CBSEENMA12033074

    Find the particular solution of (1 + x2 + y2 + x2 y2 ) dx + x y dy = 0

    Solution
    The given differential equation is
     (1 + x2 + y2 + x2 y2 ) dx + x y dy = 0
    or   open square brackets left parenthesis 1 plus straight x squared right parenthesis space plus space straight y squared left parenthesis 1 plus straight x squared right parenthesis close square brackets dx space plus space straight x space straight y space dy space equals space 0
    or   left parenthesis 1 plus straight x squared right parenthesis space left parenthesis 1 plus straight y squared right parenthesis space dx space space plus straight x space straight y space dy space equals space 0
    or                      straight x space straight y space dy space equals space minus left parenthesis 1 plus straight x squared right parenthesis thin space left parenthesis 1 plus straight y squared right parenthesis space dx
    therefore space space space space space fraction numerator straight y over denominator 1 plus straight y squared end fraction dy space equals space minus fraction numerator 1 plus straight x squared over denominator straight x end fraction dx
therefore space space space space fraction numerator straight y over denominator 1 plus straight y squared end fraction dy space equals space minus open parentheses 1 over straight x plus straight x close parentheses dx
    Integrating,   1 half integral fraction numerator 2 straight y over denominator 1 plus straight y squared end fraction dy space equals space minus integral open parentheses 1 over straight x plus straight x close parentheses space dx
    therefore space space space space 1 half space log space left parenthesis 1 plus straight y squared right parenthesis space equals space minus open square brackets log space open vertical bar straight x close vertical bar plus straight x squared over 2 close square brackets plus straight c                   ...(1)
    Now straight y space equals space 0 space space when space straight x space equals space 1
    therefore space space space space space space space space space space space space space space space 1 half log space 1 space space equals space minus open square brackets log space 1 plus 1 half close square brackets plus straight c
therefore space space space space space space space space space space space space space space space space 0 space equals space minus 1 half plus straight c space space space space space space space space space space space space space space rightwards double arrow space space space straight c space equals space 1 half
therefore space space space space from space left parenthesis 1 right parenthesis
space space space space space space space space space space space space space 1 half log space open square brackets 1 plus straight y squared close square brackets equals space minus open square brackets log space open vertical bar straight x close vertical bar plus straight x squared over 2 close square brackets plus 1 half
    which is required solution. 
    Question 244
    CBSEENMA12033075

    Find the particular solution of the differential equation log space open parentheses dy over dx close parentheses space equals space 3 straight x plus 4 straight y given that y = 0 when x = 0.

    Solution

    The given differential equation is
    log open parentheses dy over dx close parentheses space equals space 3 straight x plus 4 straight y space space space space or space space space space space dy over dx equals space straight e to the power of 3 straight x plus 4 straight y end exponent space space space or space space space space space dy over dx space equals straight e to the power of 2 straight x end exponent. space straight e to the power of 4 straight y end exponent
    Separating the variables, dy over straight e to the power of 4 straight y end exponent space equals straight e to the power of 3 straight x end exponent space dx space or space space space integral straight e to the power of negative 4 straight y end exponent dy space equals space integral straight e to the power of 3 straight x end exponent space dx
    therefore space space space fraction numerator straight e to the power of negative 4 straight y end exponent over denominator negative 4 end fraction space equals space straight e to the power of 3 straight x end exponent over 3 plus straight c                                    ...(1)
    when y = 0,  x = 0,   then from (1), we get,
                    negative straight e to the power of 0 over 4 space equals space straight e to the power of 0 over 3 plus straight c space space space space or space space space minus 1 fourth space equals space 1 third plus straight c
    therefore space space space space space space straight c space equals space minus 1 fourth minus 1 third space equals space minus 7 over 12
    therefore space space from (1),  1 fourth straight e to the power of negative 4 straight y end exponent space equals space 1 third straight e to the power of 3 straight x end exponent space minus space 7 over 12 which  is required solution. 

    Question 245
    CBSEENMA12033076

    Find the equation of the curve passing through the point (1, 1) whose differential equation is x dy = (2 x2 + 1) dx (x ≠ 0).

    Solution
    The given differential equation is
                             x dy = (2 x2 + 1) dx
    or               dy space equals space fraction numerator 2 straight x squared plus 1 over denominator straight x end fraction dx
    Integrating, integral space 1 space dy space equals space integral fraction numerator 2 straight x squared plus 1 over denominator straight x end fraction dx
    or               integral 1 space dy space equals space integral open parentheses fraction numerator 2 straight x squared over denominator straight x end fraction plus 1 over straight x close parentheses dx
    or                integral 1 space dy space equals space integral open parentheses 2 straight x plus 1 over straight x close parentheses dx
    therefore space space space space space space space space space space space space space space space space space space space space space space space space space space straight y space equals space straight x squared space plus log space open vertical bar straight x close vertical bar space plus straight c                     ...(1)
    The curve passes through (1, 1)
    therefore space space space 1 space equals space 1 plus log space open vertical bar 1 close vertical bar plus straight c space space space or space space space space 1 space equals space 1 space plus 0 plus straight c space space space space rightwards double arrow space space space straight c space space equals 0
    Putting c = 0 in (1), we get
                 straight y space equals straight x squared plus space log space open vertical bar straight x close vertical bar comma space which space is space required space solution. space
    Question 246
    CBSEENMA12033077

    Find the equation of a curve passing through the point (– 2, 3), given that the slope of the tangent to the curve at any point (x, y) is fraction numerator 2 straight y over denominator straight y squared end fraction.

    Solution
    We know that slope of tangent to a curve is given by dy over dx
    From the given condition, 
                           dy over dx space equals space fraction numerator 2 straight x over denominator straight y squared end fraction
    Separating the variables and integrating, 
                       integral straight y squared space dy space equals space 2 space integral space straight x space dx
    therefore space space space space space space space space space space space space space straight y cubed over 3 space equals space straight x squared plus straight c                             ...(1)
    Since curve passes through (-2, 3)
    therefore space space space space space space space space space space space space space space space space fraction numerator left parenthesis 3 right parenthesis cubed over denominator 3 end fraction space equals space left parenthesis negative 2 right parenthesis squared plus straight c space space space space or space space space space space space 9 space equals space 4 plus straight c space space space rightwards double arrow space space space space straight c space equals space 5
    Putting c = 5 in (1), we get,
                straight y cubed over 3 space equals space straight x squared plus 5 space space space or space space space straight y cubed space equals space 3 left parenthesis straight x squared plus 5 right parenthesis
    which is required equation of curve. 
    Question 247
    CBSEENMA12033078

    For the differential equation xy dy over dx space equals space left parenthesis straight x plus 2 right parenthesis thin space left parenthesis straight y plus 2 right parenthesis comma find the solution curve passing through the point (1, -1).

    Solution
    The given differential equation is
            straight x space straight y dy over dx space equals space left parenthesis straight x plus 2 right parenthesis thin space left parenthesis straight y plus 2 right parenthesis
    Separating the variables, we get,
                        fraction numerator straight y over denominator straight y plus 2 end fraction dy space equals space fraction numerator straight x plus 2 over denominator straight x end fraction dx
    Integrating,   integral fraction numerator straight y over denominator straight y plus 2 end fraction dy space equals space integral fraction numerator straight x plus 2 over denominator straight x end fraction dx
    therefore space space space space integral fraction numerator left parenthesis straight y plus 2 right parenthesis space minus space 2 over denominator straight y plus 2 end fraction dy space equals space integral open parentheses straight x over straight x plus 2 over straight x close parentheses dx
    therefore space space space space integral open parentheses 1 minus fraction numerator 2 over denominator straight y plus 2 end fraction close parentheses space dy space equals space integral open parentheses 1 plus 2 over straight x close parentheses dx
    therefore space space space straight y minus 2 space open vertical bar straight y plus 2 close vertical bar space equals space straight x plus 2 space log open vertical bar straight x close vertical bar space plus space straight c                       ...(1)
    Since the curve passes through (1, -1)
    therefore space space space space space minus 1 minus 2 space log space open vertical bar negative 1 plus 2 close vertical bar space equals space 1 plus 2 space log space open vertical bar 1 close vertical bar space plus space straight c
therefore space space space space space space minus 1 minus 2 space log space open vertical bar 1 close vertical bar space equals space 1 plus 2 space log space open vertical bar 1 close vertical bar plus straight c
therefore space space space minus 1 minus 2 space left parenthesis 0 right parenthesis space equals space 1 space plus space 2 left parenthesis 0 right parenthesis space plus space straight c space space space rightwards double arrow space space straight c space equals space minus 2
therefore space space space from space left parenthesis 1 right parenthesis comma space space space straight y minus 2 space log space open vertical bar straight y plus 2 close vertical bar space equals space straight x plus 2 space log space open vertical bar straight x close vertical bar space minus space 2
    or        straight y minus straight x plus 2 space equals space 2 space log space open vertical bar straight x space left parenthesis straight y plus 2 right parenthesis close vertical bar
    or           straight y minus straight x plus 2 space equals space log space open vertical bar straight x space left parenthesis straight y plus 2 right parenthesis close vertical bar squared
    or            straight y minus straight x plus 2 space equals space log space open square brackets straight x squared space left parenthesis straight y plus 2 right parenthesis squared close square brackets
    is the required solution. 
    Question 248
    CBSEENMA12033079

    Find the equation of a curve passing through the point (0, – 2) given that at any point (x, y) on the curve, the product of the slope of its tangent and y coordinate of the point is equal to the x coordinate of the point.

    Solution
    Let y = f(x) be equation of curve
    Now dy over dx is slope of tangent to the curve at point (x, y).
    From the given condition,
                              dy over dx cross times straight y space equals space straight x space space space space space space space space space space space space space space space space space space space space or space space space space space dy over dx space equals space straight x over straight y
    From the given condition,
                            dy over dx cross times straight y space equals straight x space space space space space space or space space space dy over dx space equals space straight x over straight y
    Separating the variables and integrating, 
                  integral space straight y space dy space equals space integral straight x space dx space space space space space space space space space space space or space space space space space straight y squared over 2 space equals space straight x squared over 2 plus straight c                ...(1)
    Since it passes through (0, -2)
    therefore space space space space space fraction numerator left parenthesis negative 2 right parenthesis squared over denominator 2 end fraction space equals space fraction numerator left parenthesis 0 right parenthesis squared over denominator 2 end fraction plus straight c space space space space rightwards double arrow space space space space 2 space equals space straight c
    therefore space space space from space left parenthesis 1 right parenthesis comma space space space space straight y squared over 2 space equals space straight x squared over 2 plus 2 space space space or space space space space straight y squared space equals space straight x squared plus 4
    which is required equation of curve. 
    Question 249
    CBSEENMA12033925

    Represent graphically a displacement of 40 km., 30° west of south.

    Solution
    The vector OP with rightwards arrow on top represents the required displacement. 

                             
    Question 250
    CBSEENMA12033926

    Represent graphically a displacement of 40 km. 30° cast of north.

    Solution
    The vector OP with rightwards arrow on top represents the required displacement. 
                
    Question 251
    CBSEENMA12033927

    Classify the following measures as scalars and vectors.
    (i) 5 seconds
    (ii) 1000 cm3
    (iii) 10 Newton
    (iv) 30 km hr
    (v) 10 g/cm3
    (vi) 20 m/s towards north

    Solution

    (i) Time-scalar
    (ii) Volume-scalar
    (iii) Force-vector
    (iv) Speed-scalar
    (v) Density-scalar
    (iv) Velocity-vector

    Question 252
    CBSEENMA12033928
    Question 254
    CBSEENMA12033930
    Question 255
    CBSEENMA12033931
    Question 257
    CBSEENMA12033933
    Question 258
    CBSEENMA12033934
    Question 259
    CBSEENMA12033935
    Question 260
    CBSEENMA12033936
    Question 261
    CBSEENMA12033937
    Question 262
    CBSEENMA12033938
    Question 263
    CBSEENMA12033939

    In figure, (a square), identify the following vectors.

    (i) Coinitial    
    (ii) Equal
    (iii) Collinear but not equal



    Solution

    (i) Vectors straight a with rightwards arrow on top space and space straight d with rightwards arrow on top are coinitial
    (ii) Vectors straight b with rightwards arrow on top space and space straight d with rightwards arrow on top are equal
    (iiii) Vectors straight a with rightwards arrow on top space and space straight c with rightwards arrow on top are collinear but not equal. 

    Question 264
    CBSEENMA12033940

    In given figure which of the vectors are:

    (i) Collinear      (ii) Equal    (iii) Coinitial

    Solution

    (i) Collinear vectors :   straight a with rightwards arrow on top. space straight c with rightwards arrow on top space and space straight d with rightwards arrow on top
    (ii) Equal vectors: straight a with rightwards arrow on top space and space straight c with rightwards arrow on top.
    (iii) Coinitial vectors: straight b with rightwards arrow on top. space straight c with rightwards arrow on top space and space straight d with rightwards arrow on top

    Question 266
    CBSEENMA12033942

    If open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 3 space and space space minus space 4 space less or equal than space straight k space less or equal than space 1 comma then what can you say about open vertical bar straight k space straight a with rightwards arrow on top close vertical bar ?

    Solution

    Here,             open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 3 comma space space space space minus space 4 space less or equal than space straight k space less or equal than space 1
               When            k = -4,   open vertical bar straight k space straight a with rightwards arrow on top close vertical bar space equals space open vertical bar straight k space straight a with rightwards arrow on top close vertical bar space equals space open vertical bar straight k close vertical bar space open vertical bar straight a with rightwards arrow on top close vertical bar space equals negative open vertical bar negative 4 space left enclose left parenthesis 3 end enclose right parenthesis close vertical bar space equals space 4 space cross times space 3 space equals space 12
                When            k = 1,   open vertical bar straight k space straight a with rightwards arrow on top close vertical bar space equals space open vertical bar straight k close vertical bar space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space left parenthesis 1 right parenthesis thin space left parenthesis 3 right parenthesis space equals space 3
               Also,  
                        open vertical bar straight k space straight a with rightwards arrow on top close vertical bar space space greater or equal than space 0
therefore space space space space space space 0 space less or equal than space open vertical bar straight k space straight a with rightwards arrow on top close vertical bar space less or equal than space 12.

    Question 267
    CBSEENMA12033943

    A, B and C are three collincar points such that AB with rightwards arrow on top space equals space straight a with rightwards arrow on top space and space BC with rightwards arrow on top space equals straight b with rightwards arrow on top. Find the vector AC with rightwards arrow on top.

    Solution

    We have AC with rightwards arrow on top space equals space AB with rightwards arrow on top space plus space BC with rightwards arrow on top
    therefore            AC with rightwards arrow on top space equals space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top

    Question 268
    CBSEENMA12033944

    straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are two non-collinear vectors having the same initial point. What vectorn is represented by straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top?

    Solution

    Let   OA with rightwards arrow on top space equals space straight a with rightwards arrow on top comma space space space OB with rightwards arrow on top space equals space straight b with rightwards arrow on top
    therefore space space space space space space AC with rightwards arrow on top space equals space OB with rightwards arrow on top space equals space straight b with rightwards arrow on top
    Now,   OC with rightwards arrow on top space equals space OA with rightwards arrow on top space plus space AC with rightwards arrow on top
     therefore space space space space OC with rightwards arrow on top space equals space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top
    therefore space space space space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top is the vector represented by the diagonal OC.

    Question 269
    CBSEENMA12033945

    The position vectors of points A. B, C. D) are straight a with rightwards arrow on top comma space space straight b with rightwards arrow on top comma space space 2 space straight a with rightwards arrow on top space plus space 3 space straight b with rightwards arrow on top  and  straight a with rightwards arrow on top space minus space 2 space straight b with rightwards arrow on top respectively, show that AC with rightwards arrow on top space equals space straight a with rightwards arrow on top space plus space 3 space straight b with rightwards arrow on top space and space DB with rightwards arrow on top space equals space 3 space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top

    Solution

    Here P.V. of straight A space equals space straight a with rightwards arrow on top.     P.V. of B = straight b with rightwards arrow on top,     P.V. of C = 2 space straight a with rightwards arrow on top space plus space 3 space straight b with rightwards arrow on top.
                       P.V. of  D = straight a with rightwards arrow on top space minus space 2 space straight b with rightwards arrow on top
              therefore space space space space space AC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight A space equals space open parentheses 2 space stack straight a space with rightwards arrow on top space plus space 3 space straight b with rightwards arrow on top close parentheses space minus space straight a with rightwards arrow on top space equals space straight a with rightwards arrow on top space plus space 3 space straight b with rightwards arrow on top
space space space space space space space space space space space space DB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight D space equals space straight b with rightwards arrow on top space minus space left parenthesis straight a with rightwards arrow on top space minus space 2 space straight b with rightwards arrow on top right parenthesis space equals space 3 space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top

    Question 270
    CBSEENMA12033946

    Vectors drawn from the origin to the points A, B and C are respectively straight a with rightwards arrow on top. space straight b with rightwards arrow on top space and space 4 space straight a with rightwards arrow on top space space minus space 3 space straight b with rightwards arrow on top. Find AC with rightwards arrow on top space and space BC with rightwards arrow on top.

    Solution

    Let O be origin of vectors. Then
                              OA with rightwards arrow on top space equals straight a with rightwards arrow on top comma space space OB with rightwards arrow on top space equals space straight b with rightwards arrow on top comma space space OC with rightwards arrow on top space equals space 4 space straight a with rightwards arrow on top space minus space 3 space straight b with rightwards arrow on top
    Now,              AC with rightwards arrow on top space equals space OC with rightwards arrow on top space minus space OA with rightwards arrow on top space equals space open parentheses 4 space straight a with rightwards arrow on top minus space 3 space straight b with rightwards arrow on top close parentheses space minus space straight a with rightwards arrow on top space equals space 3 space straight a with rightwards arrow on top space minus space 3 space straight b with rightwards arrow on top
    and                BC with rightwards arrow on top space equals space OC with rightwards arrow on top space minus space OB with rightwards arrow on top space equals space left parenthesis 4 space straight a with rightwards arrow on top space minus space 3 space straight b with rightwards arrow on top right parenthesis space minus space straight b with rightwards arrow on top space equals space 4 space straight a with rightwards arrow on top space minus space 4 space straight b with rightwards arrow on top

    Question 271
    CBSEENMA12033947

    Give a condition that the three vectors straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top form the three sides of a triangle. What are the other possibilities?

    Solution

    Let OA with rightwards arrow on top space equals space straight a with rightwards arrow on top comma space space AB with rightwards arrow on top space equals space straight b with rightwards arrow on top comma space space space BO with rightwards arrow on top space equals space straight c with rightwards arrow on top
    Now,     OA with rightwards arrow on top space plus space AB with rightwards arrow on top space equals space OB with rightwards arrow on top
    therefore space space space space space space space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space equals space minus straight c with rightwards arrow on top
therefore space space space space space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top
    Other possibilities are
                     straight a with rightwards arrow on top space equals space straight b with rightwards arrow on top plus straight c with rightwards arrow on top comma space
                     straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top space plus space straight a with rightwards arrow on top comma space space space straight c with rightwards arrow on top space equals space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top

    Other possibilities are
                        straight a with rightwards arrow on top space equals space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top comma
straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top space plus space straight a with rightwards arrow on top comma space space straight c with rightwards arrow on top space equals space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top

    Question 272
    CBSEENMA12033948

    ABCD is a parallelogram. If AB with rightwards arrow on top space equals space straight a with rightwards arrow on top comma space space space BC with rightwards arrow on top space equals space straight b with rightwards arrow on top comma space   then
    (i)    Show that AC with rightwards arrow on top space equals straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top comma space space space space BD with rightwards arrow on top space equals space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top.
    (ii) What is the geometrical significance of the relation
                          open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar ?

    Solution

    Here AB with rightwards arrow on top space equals space stack straight a comma with rightwards arrow on top space space BC with rightwards arrow on top space equals space straight b with rightwards arrow on top
    (i) In increment ABC comma space space AC with rightwards arrow on top space equals space AB with rightwards arrow on top space plus space BC with rightwards arrow on top space equals space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top
    In increment ABD comma space space AB with rightwards arrow on top space plus space BD with rightwards arrow on top space equals space AD with rightwards arrow on top
       therefore space space space space BD with rightwards arrow on top space equals space AD with rightwards arrow on top space minus space AB with rightwards arrow on top space equals space BC with rightwards arrow on top space minus space AB with rightwards arrow on top                                                  open square brackets because space space space AD with rightwards arrow on top space equals space BC with rightwards arrow on top close square brackets

                             equals space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top
    (ii)
           open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar
    rightwards double arrow space space space space space open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top close vertical bar space as space open vertical bar negative straight a with rightwards arrow on top close vertical bar space equals space open vertical bar straight a with rightwards arrow on top close vertical bar
therefore space space space space space space space space open vertical bar AC with rightwards arrow on top close vertical bar space equals space open vertical bar BD with rightwards arrow on top close vertical bar
rightwards double arrow space space space space space space space space space space AC space equals space BD space space space space space space space space space space space space space space space space space space rightwards double arrow space space space space space space diagonals space of space vertical line vertical line space gm space ABCD space are space equal
therefore space space space space space geometrically space open vertical bar straight a plus straight b close vertical bar space equals open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar space means space ABCD space is space straight a space rectangle. space

    Question 273
    CBSEENMA12033949

    Let straight u with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top comma space space straight v with rightwards arrow on top space equals space minus 2 space straight i with hat on top space plus space straight j with hat on top space and space straight w with rightwards arrow on top space equals space 4 straight i with hat on top space plus space 3 space straight j with hat on top. Find scalars a and b such that straight w with rightwards arrow on top space equals space straight a straight u with rightwards arrow on top space plus space straight b space straight v with rightwards arrow on top.

    Solution

    Here,    straight u with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top comma space space straight v with rightwards arrow on top space equals space minus 2 space straight i with hat on top space plus space straight j with hat on top comma space space straight w with rightwards arrow on top space equals space 4 space straight i with hat on top space plus space 3 space straight j with hat on top
    therefore                                       straight w with rightwards arrow on top space equals space straight a straight u with rightwards arrow on top space plus space straight b space straight v with rightwards arrow on top.
    rightwards double arrow space space space space space space 4 space straight i with hat on top space plus space 3 space straight j with hat on top space equals space straight a space open parentheses straight i with hat on top space plus space 2 space straight j with hat on top close parentheses space plus space straight b space open parentheses negative 2 space straight i with hat on top space plus space straight j with hat on top close parentheses
rightwards double arrow space space space left parenthesis straight a minus 2 straight b minus 4 right parenthesis space straight i with hat on top space plus space left parenthesis 2 straight a plus straight b minus 3 right parenthesis space straight j with hat on top space equals space 0 with rightwards arrow on top
rightwards double arrow space space space space space space space space space space straight a minus 2 straight b minus 4 space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
rightwards double arrow space space space space space space space space 2 straight a plus straight b minus 3 space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis
Solving space left parenthesis 1 right parenthesis space and space left parenthesis 2 right parenthesis comma space we space get
space space space space space space space space space space space space space space space fraction numerator straight a over denominator 6 plus 4 end fraction space equals fraction numerator straight b over denominator negative 8 plus 3 end fraction space equals fraction numerator 1 over denominator 1 plus 4 end fraction
therefore space space space space space space space space straight a over 10 space equals fraction numerator straight b over denominator negative 5 end fraction space equals 1 fifth
therefore space space space space space space space space space straight a space equals space 10 over 5 space equals 2 comma space space space space straight b space equals space fraction numerator negative 5 over denominator 5 end fraction space equals space minus 1 space space

    Question 274
    CBSEENMA12033950

    If P1 , P2, P3, P4 are points in a plane or space and O, the origin of vectors, show that P4 coincides with O if an only if 
    stack OP subscript 1 with rightwards arrow on top space plus space stack straight P subscript 1 straight P subscript 2 with rightwards arrow on top space plus space stack straight P subscript 2 straight P subscript 3 with rightwards arrow on top space plus space stack straight P subscript 3 straight P subscript 4 with rightwards arrow on top space equals space 0 with rightwards arrow on top.

    Solution
    stack OP subscript 1 with rightwards arrow on top space plus space stack straight P subscript 1 straight P subscript 2 with rightwards arrow on top space plus space stack straight P subscript 2 straight P subscript 3 with rightwards arrow on top space equals space stack straight P subscript 3 straight P subscript 4 with rightwards arrow on top space equals space 0 with rightwards arrow on top.
                    left right double arrow space space space open parentheses stack OP subscript 1 space with rightwards arrow on top plus stack straight P subscript 1 straight P subscript 2 with rightwards arrow on top close parentheses space plus space open parentheses stack straight P subscript 2 straight P subscript 3 with rightwards arrow on top space plus space stack straight P subscript 3 straight P subscript 4 with rightwards arrow on top close parentheses space equals space 0 with rightwards arrow on top
left right double arrow space space space stack OP subscript 2 with rightwards arrow on top space plus space stack straight P subscript 2 straight P subscript 4 with rightwards arrow on top space equals space 0 with rightwards arrow on top space space space space space left right double arrow space space space space space space space stack OP subscript 4 with rightwards arrow on top space equals space 0 with rightwards arrow on top space space space space left right double arrow space space straight O space and space straight P subscript 4 space coincide.
                   
                     

                      
    Question 275
    CBSEENMA12033951

    PQRS is a parallelogram. If straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top are the position vectors of the vertices P, Q and R respectively with reference to the origin of reference O ; find the position vector of S with reference to O.

    Solution

    We have QP with rightwards arrow on top space equals space straight P. straight V. space of space straight P space minus space straight P. straight V. space of space straight Q space equals space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top
                         But space RS with rightwards arrow on top space equals space QP with rightwards arrow on top space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space space space PQRS space is space straight a space vertical line vertical line space gm close square brackets
    therefore space space space space space space space space space space space space RS with rightwards arrow on top space equals space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top
    Now position vector of S with reference to O = OS with rightwards arrow on top
                                   equals space OR with rightwards arrow on top space plus space RS with rightwards arrow on top space equals space straight c with rightwards arrow on top space plus space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top

    Question 276
    CBSEENMA12033952

    If straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are the vectors determined by two adjacent sides of a regular hexagon, find the vectors determined by the other sides taken in order.

    Solution
    Let ABCDHF be a regular hexagon such that
                             AB with rightwards arrow on top space equals space space straight a with rightwards arrow on top comma space space space BC with rightwards arrow on top space equals space straight b with rightwards arrow on top
    Now,           AC with rightwards arrow on top equals space AB with rightwards arrow on top space plus space BC with rightwards arrow on top space equals space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top
                         AD with rightwards arrow on top space equals space 2 space BC with rightwards arrow on top space space space space space space space space space space space space space space space space space space space space space space open square brackets because space AD space equals space 2 space BC space and space AD thin space vertical line vertical line thin space BC close square brackets

    therefore space space space space space space space AD with rightwards arrow on top space equals space 2 space straight b with rightwards arrow on top
               In increment ADC. space space AC with rightwards arrow on top space plus space CD with rightwards arrow on top space equals space AD with rightwards arrow on top
          therefore space space space space space CD with rightwards arrow on top space equals space AD with rightwards arrow on top space minus space AC with rightwards arrow on top space equals space 2 straight b with rightwards arrow on top space minus space left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis space equals space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top
                  DE with rightwards arrow on top space equals space minus AB with rightwards arrow on top space equals space minus straight a with rightwards arrow on top
EF with rightwards arrow on top space equals space minus BC with rightwards arrow on top space equals space minus straight b with rightwards arrow on top
FA with rightwards arrow on top space equals space minus CD with rightwards arrow on top space equals space minus left parenthesis straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top right parenthesis space equals space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top
              
    Question 277
    CBSEENMA12033953

    If straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top be the vectors represented by the sides of a triangle, taken in order, then prove that straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top.

    Solution

    Let ABC be a triangle such that 
               BC with rightwards arrow on top space equals space straight a with rightwards arrow on top. space space CA with rightwards arrow on top space equals space straight b with rightwards arrow on top space. space AB with rightwards arrow on top space equals space straight c with rightwards arrow on top
    L.H.S. = straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top
               equals space BC with rightwards arrow on top space plus space CA with rightwards arrow on top space plus space AB with rightwards arrow on top space equals space open parentheses BC with rightwards arrow on top space plus space CA with rightwards arrow on top close parentheses space plus space AB with rightwards arrow on top
                 equals space BA with rightwards arrow on top space plus space AB with rightwards arrow on top

                                                                open square brackets because space space space BC with rightwards arrow on top space plus space CA with rightwards arrow on top space equals AB with rightwards arrow on top space by space triangle space law space of space addition close square brackets
                     equals space AB with rightwards arrow on top space plus space AB with rightwards arrow on top space space equals space 0 with rightwards arrow on top space equals space straight R. straight H. straight S.
therefore space space space space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top space space equals space 0 with rightwards arrow on top. space
                 

    Question 278
    CBSEENMA12033954

    If AO with rightwards arrow on top space plus space OB with rightwards arrow on top space equals space BO with rightwards arrow on top space plus space OC with rightwards arrow on top comma space then prove that the points A, B and C are collinear.

    Solution

    We have AO with rightwards arrow on top space plus space OB with rightwards arrow on top space equals space BO with rightwards arrow on top space plus space OC with rightwards arrow on top
    therefore space space space space space space space space AB with rightwards arrow on top space equals space BC with rightwards arrow on top
    ( Triangle Law of Vectors)
    therefore space space space space space AB with rightwards arrow on top space and space BC with rightwards arrow on top space are parallel vectors. 
    But B is the common point . 
    therefore space space space space space AB with rightwards arrow on top space and space BC with rightwards arrow on top are along the same line
    ∴ point A, B and C are collinear.

    Question 279
    CBSEENMA12033955

    Prove that the line joining the middle points of two sides of a triangle is parallel to the third side and is half of it.

    Solution
    Let D, E be mid-points of sides AB and AC of the ∆ ABC.
    therefore          DE with rightwards arrow on top space equals space DA with rightwards arrow on top space plus space AE with rightwards arrow on top
    [By Triangle Law of Vectors in increment thin space ADE]
                                 equals space 1 half BA with rightwards arrow on top space plus space 1 half AC with rightwards arrow on top space equals space 1 half left parenthesis BA with rightwards arrow on top space plus space AC with rightwards arrow on top right parenthesis
therefore space space space DE with rightwards arrow on top space equals space 1 half space BC with rightwards arrow on top
    therefore space space space space space space space DE thin space vertical line vertical line thin space BC space and space DE space equals space 1 half BC.

    Hence the result. 
    Question 280
    CBSEENMA12033956

    ABC is a triangle and D is the mid-point of the side BC. Show that AB with rightwards arrow on top space plus space AC with rightwards arrow on top space equals space 2 space AD with rightwards arrow on top.

    Solution

    In increment ABD comma space space space space space space space space space space space space space space space space space space AB with rightwards arrow on top space equals space AD with rightwards arrow on top space plus space BD with rightwards arrow on top                                    ...(1)
    In  increment space ADC comma space space space space space space AC with rightwards arrow on top space equals space AD with rightwards arrow on top space plus space DC with rightwards arrow on top                                            ...(2)
    Adding (1) and (2),  we get

         AB with rightwards arrow on top space plus space AC with rightwards arrow on top space equals space 2 space AD with rightwards arrow on top space plus space open parentheses DB with rightwards arrow on top space plus space DC with rightwards arrow on top close parentheses
                                                   equals space 2 space AD with rightwards arrow on top space plus space DB with rightwards arrow on top space space space space space space space space space space space space space space space space space space space space space space open square brackets because space space straight D space is space mid minus point space of space BC comma space space space space space because space space BD with rightwards arrow on top space equals DC with rightwards arrow on top close square brackets
equals space 2 space stack AD space with rightwards arrow on top space minus space BD with rightwards arrow on top space plus space BD with rightwards arrow on top
    therefore     AB with rightwards arrow on top space plus space AC with rightwards arrow on top space equals 2 space space AD with rightwards arrow on top

          

    Question 281
    CBSEENMA12033957

    If D and E are the mid-points of sides AB and AC of a triangle ABC respectively show that
    BE with rightwards arrow on top space plus space DC with rightwards arrow on top space equals space 3 over 2 BC with rightwards arrow on top.

    Solution

    Take A is origin. Let straight b with rightwards arrow on top comma space straight c with rightwards arrow on top be position vectors of B, C respectively so that
    AD with rightwards arrow on top space equals space 1 half space straight b with rightwards arrow on top comma space space space AE with rightwards arrow on top space equals 1 half straight c with rightwards arrow on top
    L.H.S.  = BE with rightwards arrow on top space plus space DC with rightwards arrow on top  
                                      = (P.V. Of E - P.V. of B) + (P.V. of C - P.V. of D)

                          equals space open parentheses 1 half straight c with rightwards arrow on top space minus straight b with rightwards arrow on top close parentheses space plus space open parentheses straight c with rightwards arrow on top minus 1 half straight b with rightwards arrow on top close parentheses space equals space 3 over 2 straight c with rightwards arrow on top space minus space 3 over 2 straight b with rightwards arrow on top
equals space 3 over 2 left parenthesis straight c with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space equals space 3 over 2 BC with rightwards arrow on top space equals space straight R. straight H. straight S.

    Question 282
    CBSEENMA12033958

    If straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top space and space straight d with rightwards arrow on top are distinct non-zero vectors represented by directed lines from the origin to the points A, B, C and D respectively and if straight b with rightwards arrow on top minus straight a with rightwards arrow on top space equals space straight c with rightwards arrow on top space minus space straight d with rightwards arrow on top, then prove that ABCD is a parallelogram.

    Solution

    Here  straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top comma space straight d with rightwards arrow on top are the position vectors of A, B, C, D respectively with reference to O as origin
    Now,             straight b with rightwards arrow on top minus straight a with rightwards arrow on top space equals space straight c with rightwards arrow on top minus straight d with rightwards arrow on top
    rightwards double arrow space space space space space space OB with rightwards arrow on top space minus space OA with rightwards arrow on top space equals space OC with rightwards arrow on top space minus space OD with rightwards arrow on top
rightwards double arrow space space space space space space space space space space space AB with rightwards arrow on top space equals space DC with rightwards arrow on top
therefore space space space space space space AB space equals space DC space and space AB vertical line vertical line DC
therefore space space space space space ABCD space is space straight a space parallelogram.

    Question 283
    CBSEENMA12033959

    Let O be the centre of regular hexagon ABCDEF. Find the sum.
    OA with rightwards arrow on top space plus space OB with rightwards arrow on top space plus space OC with rightwards arrow on top space plus space OD with rightwards arrow on top space plus space stack OE space with rightwards arrow on top space plus space OF with rightwards arrow on top
.

    Solution

    We have
                    OA with rightwards arrow on top space equals space minus OD with rightwards arrow on top. space space OB with rightwards arrow on top space equals space minus OE with rightwards arrow on top
stack OC space with rightwards arrow on top space equals space minus OF with rightwards arrow on top
    therefore space space space space OA with rightwards arrow on top space plus space OD with rightwards arrow on top space equals space 0 with rightwards arrow on top                                 ...(1)
              OB with rightwards arrow on top space plus space OE with rightwards arrow on top space equals space 0 with rightwards arrow on top                                ...(2)
              OC with rightwards arrow on top space plus space OF with rightwards arrow on top space equals 0 with rightwards arrow on top                                  ...(3)
    Adding (1), (2), (3), we get,
                          OA with rightwards arrow on top space plus space OB with rightwards arrow on top space plus OC with rightwards arrow on top space plus space OD with rightwards arrow on top space plus space OE with rightwards arrow on top space plus space OF with rightwards arrow on top space equals space 0 with rightwards arrow on top
               

    Question 284
    CBSEENMA12033960

    Show that the diagonals a quadrilateral bisect each other if and only if it is a parallelogram.

    Solution

    Let ABCD be the quadrilateral and O be the point of intersection of the diagonals AC and BD. Let OA with rightwards arrow on top space equals space straight a with rightwards arrow on top space and space OB with rightwards arrow on top space equals space straight b with rightwards arrow on top. O is the midpoint of both AC and BD if and only if DO with rightwards arrow on top space equals space straight b with rightwards arrow on top space and space CO with rightwards arrow on top space equals space straight a with rightwards arrow on top or if and only if DA with rightwards arrow on top space equals space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top space and space CB with rightwards arrow on top space equals space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top comma i.e., if any only if DA with rightwards arrow on top space equals space CB with rightwards arrow on top. We also know that a quadrilateral is a parallelogram if and only if its opposite sides are equal and parallel.
    Hence the result follows.

    Question 285
    CBSEENMA12033961

    Show that the points straight a with rightwards arrow on top space minus space 2 space straight b with rightwards arrow on top space plus space 3 space straight c with rightwards arrow on top comma space space space space 2 space straight a with rightwards arrow on top space plus space 3 space straight b with rightwards arrow on top space minus space 4 space straight c with rightwards arrow on top comma space minus 7 space straight b with rightwards arrow on top space plus space 10 space straight c with rightwards arrow on top are collinear, where straight a with rightwards arrow on top comma space space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top are three non-coplanar vectors. 

    Solution

    Let straight a with rightwards arrow on top space minus space 2 straight b with rightwards arrow on top space plus space 3 space straight c with rightwards arrow on top comma space space 2 space straight a with rightwards arrow on top space plus space 3 space straight b with rightwards arrow on top space minus space 4 space straight c with rightwards arrow on top comma space space minus 7 space straight b with rightwards arrow on top space plus space 10 space straight c with rightwards arrow on top be position vectors of A, B and C respectively. 
               Now,     AB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A space equals space open parentheses 2 space straight a with rightwards arrow on top space plus space 3 space straight b with rightwards arrow on top space minus space 4 space straight c with rightwards arrow on top close parentheses space minus space open parentheses straight a with rightwards arrow on top space minus space 2 space straight b with rightwards arrow on top space plus space 3 space straight c with rightwards arrow on top close parentheses
              therefore space space space AB with rightwards arrow on top space equals space straight a with rightwards arrow on top space plus space 5 space straight b with rightwards arrow on top space minus space 7 space straight c with rightwards arrow on top
    Now,      AC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight A
                          equals space open parentheses negative 7 space straight b with rightwards arrow on top space plus space 10 space straight c with rightwards arrow on top close parentheses space minus space open parentheses straight a with rightwards arrow on top space minus space 2 space straight b with rightwards arrow on top space plus space 3 space straight c with rightwards arrow on top close parentheses space equals space minus straight a with rightwards arrow on top space minus space 5 space straight b with rightwards arrow on top space plus space 7 space straight c with rightwards arrow on top
    therefore space space space space AC with rightwards arrow on top space equals space minus AB with rightwards arrow on top space space space space rightwards double arrow space space space space AB with rightwards arrow on top space and space space AC with rightwards arrow on top space are space parallel space vectors
    But these vectors have the same initial point 
    ∴     point A, B and C are collinear.

    Question 286
    CBSEENMA12033962

    Show that the points negative 2 space straight a with rightwards arrow on top space plus space 3 space straight b with rightwards arrow on top space plus space 5 space straight c with rightwards arrow on top comma space space straight a with rightwards arrow on top space plus space 2 space straight b with rightwards arrow on top space plus space 3 space straight c with rightwards arrow on top comma space space 7 space straight a with rightwards arrow on top space minus space straight c with rightwards arrow on top are collinear, where straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top are three non-coplanar vectors.

    Solution

    Let negative 2 space straight a with rightwards arrow on top space plus space 3 space straight b with rightwards arrow on top space plus space 5 space straight c with rightwards arrow on top comma space space straight a with rightwards arrow on top space plus space 2 space straight b with rightwards arrow on top space plus space 3 space straight c with rightwards arrow on top comma space space 7 space straight a with rightwards arrow on top space minus space straight c with rightwards arrow on top be the position vectors of A, B and C respectively.
    AB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A space equals space open parentheses straight a with rightwards arrow on top space plus space 2 straight b with rightwards arrow on top space plus space 3 straight c with rightwards arrow on top close parentheses space minus space open parentheses negative 2 straight a with rightwards arrow on top space plus space 3 straight b with rightwards arrow on top space plus space 5 straight c with rightwards arrow on top close parentheses space equals space 3 straight a with rightwards arrow on top minus straight b with rightwards arrow on top minus 2 straight c with rightwards arrow on top
    Also, AC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight A space equals space open parentheses 7 straight a with rightwards arrow on top space minus space straight c with rightwards arrow on top close parentheses space minus space open parentheses negative 2 straight a with rightwards arrow on top space plus space 3 straight b with rightwards arrow on top space plus space 5 straight c with rightwards arrow on top close parentheses space equals space 9 straight a with rightwards arrow on top minus straight b with rightwards arrow on top minus 2 straight c with rightwards arrow on top
                                               equals space 3 space open parentheses 3 straight a with rightwards arrow on top space minus straight b with rightwards arrow on top space minus space 2 space straight c with rightwards arrow on top close parentheses
    therefore space space space space AC with rightwards arrow on top space equals 3 space AB with rightwards arrow on top
rightwards double arrow space space space space AB with rightwards arrow on top space and space AC with rightwards arrow on top space are space parallel space vectors
    But the vectors have the same initial point point A, B and C are collinear.

    Question 287
    CBSEENMA12033963

    If A and B are two points in space and if they become respectively A', B' on a translation, show that AB with rightwards arrow on top space equals space stack straight A apostrophe space straight B apostrophe with rightwards arrow on top

    Solution
    After translation, the positions of A, B are . A', B’ respectively.
    therefore space space space space AA apostrophe space equals space BB apostrophe space and space AA apostrophe space vertical line vertical line thin space BB apostrophe
therefore space space space ABB apostrophe straight A apostrophe space is space straight a space space parllelogram
therefore space space space AB space equals space straight A apostrophe straight B apostrophe space and space AB vertical line vertical line straight A apostrophe straight B apostrophe
rightwards double arrow space space space space AB with rightwards arrow on top space equals stack straight A apostrophe space straight B apostrophe with rightwards arrow on top.

    Question 288
    CBSEENMA12033964

    ABC is a triangle and P any point in BC. If PQ with rightwards arrow on top is the sum of AP with rightwards arrow on top comma space PB with rightwards arrow on top comma space PC with rightwards arrow on top comma show that ABQC is a || gm and Q. therefore a fixed point.

    Solution

    Here PQ with rightwards arrow on top space equals space AP with rightwards arrow on top space plus space PB with rightwards arrow on top space plus space PC with rightwards arrow on top                                  (given)
    therefore space space space PQ with rightwards arrow on top space minus space PC with rightwards arrow on top space equals space AP with rightwards arrow on top space plus space PB with rightwards arrow on top
therefore space space PQ with rightwards arrow on top plus space CP with rightwards arrow on top space equals space AP with rightwards arrow on top space plus space PB with rightwards arrow on top
therefore space space space space space CQ with rightwards arrow on top space equals space AB with rightwards arrow on top space space space space space space space space space space space space rightwards double arrow space space space space CQ space equals space AB space and space CQ space vertical line vertical line thin space AB
    ∴ ABQC is a parallelogram
    But A. B, C are given to be fixed points and ABQC is a || gm
    ∴ Q is a fixed point.

    Question 289
    CBSEENMA12033965

    ABCD is a quadrilateral and O is any point in its plane. Show that it OA with rightwards arrow on top space plus space OB with rightwards arrow on top space plus space OC with rightwards arrow on top space plus space OD with rightwards arrow on top space equals space 0 with rightwards arrow on top then O is the point of intersection of lines joining the middle points of the opposite sides of ABCD.

    Solution

    Let E. F, G, H be mid-points of the sides AB. BC. CD. DA respectively of quadrilateral ABCD.
    ∴    EFGH is a || gm    [From Co-ordinate Geometry]
    ∴  diagonals EG and FH bisect each other at P (say)
    Now,    OA with rightwards arrow on top space plus space OB with rightwards arrow on top space plus space OC with rightwards arrow on top space plus space OD with rightwards arrow on top space equals space 0 with rightwards arrow on top
    rightwards double arrow space space space open parentheses OA with rightwards arrow on top space plus space OB with rightwards arrow on top close parentheses space plus space open parentheses OC with rightwards arrow on top space plus space OD with rightwards arrow on top close parentheses space equals 0 with rightwards arrow on top
rightwards double arrow space space space space 2. space OE with rightwards arrow on top space plus space space 2 space OG with rightwards arrow on top space equals space 0 with rightwards arrow on top space space space space rightwards double arrow space space space space OE with rightwards arrow on top space plus space OG with rightwards arrow on top space equals space 0 with rightwards arrow on top
rightwards double arrow space space space space space 2 space OP with rightwards arrow on top space equals space 0 with rightwards arrow on top space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space space straight P space is space the space mid minus point space of space EG close square brackets
rightwards double arrow space space space space space space space OP with rightwards arrow on top space equals space 0 with rightwards arrow on top

    ∴    O coincides with P which is the point of intersection of lines joining the middle points of the opposite sides of ABCD.

    Question 290
    CBSEENMA12033966

    For any two vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top, prove that
    (i)        open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar space less or equal than space open vertical bar straight a with rightwards arrow on top close vertical bar space plus space open vertical bar straight b with rightwards arrow on top close vertical bar              (ii)     open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar space less or equal than space open vertical bar straight a with rightwards arrow on top close vertical bar space plus space open vertical bar straight b with rightwards arrow on top close vertical bar         (iii) open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar space space space greater-than or slanted equal to space space open vertical bar straight a with rightwards arrow on top close vertical bar space minus space open vertical bar straight b with rightwards arrow on top close vertical bar

    Solution
    Case I,   straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are non-collinear vectors. 
                        Let OA with rightwards arrow on top space equals space straight a with rightwards arrow on top comma space space AB with rightwards arrow on top space equals straight b with rightwards arrow on top
    therefore space space space space space space space OB with rightwards arrow on top space equals OA with rightwards arrow on top space plus space AB with rightwards arrow on top space equals space straight a with rightwards arrow on top space plus straight b with rightwards arrow on top
Now space space space OA space equals space open vertical bar straight a with rightwards arrow on top close vertical bar comma space space AB space equals space open vertical bar straight b with rightwards arrow on top close vertical bar comma
space space space space space space space space space space space space OB space equals space open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar
       We know that in a triangle sum of two sides of triangle is always >  third side
                 therefore space space space space space space space OA plus AB greater than OB
rightwards double arrow space space space space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space plus space open vertical bar straight b with rightwards arrow on top close vertical bar space greater than space space space open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar
therefore space space space space space space space space open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar space less than space space open vertical bar straight a with rightwards arrow on top close vertical bar space plus space open vertical bar straight b with rightwards arrow on top close vertical bar


    Case II.     straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are collinear vectors.
        Let OA with rightwards arrow on top space equals space straight a with rightwards arrow on top comma space space space AB with rightwards arrow on top space equals space straight b with rightwards arrow on top space then space OB with rightwards arrow on top space equals space OA with rightwards arrow on top space plus space AB with rightwards arrow on top space equals space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top
         Also,   OA space equals space open vertical bar straight a with rightwards arrow on top close vertical bar comma space space space AB space equals open vertical bar straight b with rightwards arrow on top close vertical bar comma space space space OB space equals space open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar
        Now,    OB space equals space OA plus AB
    therefore space space space space space space open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight a with rightwards arrow on top close vertical bar space plus space open vertical bar straight b with rightwards arrow on top close vertical bar
    Combining the results of Case I and II,  we get,
                               open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar space less or equal than space space open vertical bar straight a with rightwards arrow on top close vertical bar space plus space open vertical bar straight b with rightwards arrow on top close vertical bar
    Combining the results of Case I and II, we get,
                                   open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar space less or equal than space open vertical bar straight a with rightwards arrow on top close vertical bar space plus space open vertical bar straight b with rightwards arrow on top close vertical bar
    (ii)                     open vertical bar straight a with rightwards arrow on top minus straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight a with rightwards arrow on top plus left parenthesis negative straight b with rightwards arrow on top right parenthesis close vertical bar space less or equal than space open vertical bar straight a with rightwards arrow on top close vertical bar space plus space open vertical bar negative straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight a with rightwards arrow on top close vertical bar space plus space open vertical bar straight b with rightwards arrow on top close vertical bar
    therefore                  open vertical bar straight a with rightwards arrow on top minus straight b with rightwards arrow on top close vertical bar space less or equal than open vertical bar straight a with rightwards arrow on top close vertical bar space plus space open vertical bar straight b with rightwards arrow on top close vertical bar
    (iii)          open vertical bar straight a with rightwards arrow on top close vertical bar space equals space open vertical bar left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space plus space straight b with rightwards arrow on top close vertical bar space less or equal than space open vertical bar stack straight a space with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar space plus space open vertical bar straight b with rightwards arrow on top close vertical bar
    therefore space space space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space minus space open vertical bar straight b with rightwards arrow on top close vertical bar space less or equal than space space open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar
rightwards double arrow space space space space space space space open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar space greater or equal than space space open vertical bar straight a with rightwards arrow on top close vertical bar space minus space open vertical bar straight b with rightwards arrow on top close vertical bar.
    Question 291
    CBSEENMA12033967

    If straight c with rightwards arrow on top space equals space 3 straight a with rightwards arrow on top space plus space 4 straight b with rightwards arrow on top and 2 straight c with rightwards arrow on top space equals space straight a with rightwards arrow on top space minus space 3 straight b with rightwards arrow on top, show that
    (i) straight c with rightwards arrow on top space and space straight a with rightwards arrow on top have the same direction and open vertical bar straight c with rightwards arrow on top close vertical bar space greater than space open vertical bar straight a with rightwards arrow on top close vertical bar
    (ii) straight c with rightwards arrow on top space and space straight b with rightwards arrow on top have opposite direction and 

    Solution

    Here straight c with rightwards arrow on top space equals space 3 space straight a with rightwards arrow on top space plus space 4 space straight b with rightwards arrow on top and 2 space straight c with rightwards arrow on top space equals space straight a with rightwards arrow on top space minus space 3 space straight b with rightwards arrow on top
    therefore space space space 2 space left parenthesis 3 space straight a with rightwards arrow on top space plus space 4 space straight b with rightwards arrow on top right parenthesis space equals space straight a with rightwards arrow on top minus space 3 space straight b with rightwards arrow on top space space space space rightwards double arrow space space space 6 space straight a with rightwards arrow on top space plus space 8 space straight b with rightwards arrow on top space equals space straight a with rightwards arrow on top space minus space 3 space straight b with rightwards arrow on top
    rightwards double arrow space space space 5 space straight a with rightwards arrow on top space equals space minus 11 space straight b with rightwards arrow on top
therefore space space space space straight a with rightwards arrow on top space equals space minus 11 over 5 straight b with rightwards arrow on top space and space straight b with rightwards arrow on top space equals space minus 5 over 11 straight a with rightwards arrow on top space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
    (i)    straight c with rightwards arrow on top space equals space 3 space straight a with rightwards arrow on top space plus space 4 space straight b with rightwards arrow on top space equals space 3 space straight a with rightwards arrow on top space plus space 4 space open parentheses negative 5 over 11 straight a with rightwards arrow on top close parentheses                             open square brackets because space space of space left parenthesis 1 right parenthesis close square brackets
               equals space 3 space straight a with rightwards arrow on top space minus space 20 over 11 space straight a with rightwards arrow on top space equals space 13 over 11 straight a with rightwards arrow on top

    Also,     open vertical bar straight c with rightwards arrow on top close vertical bar space equals space 13 over 11 open vertical bar straight a with rightwards arrow on top close vertical bar space space space space rightwards double arrow space space space space space space space open vertical bar straight c with rightwards arrow on top close vertical bar space greater than space open vertical bar straight a with rightwards arrow on top close vertical bar.
    (ii) straight c with rightwards arrow on top space equals space 3 space straight a with rightwards arrow on top space plus space 4 space straight b with rightwards arrow on top space equals space 3 space open parentheses negative 11 over 5 straight b with rightwards arrow on top close parentheses space plus space 4 space straight b with rightwards arrow on top                     open square brackets because space space of space left parenthesis 1 right parenthesis close square brackets
           equals space minus 33 over 5 straight b with rightwards arrow on top space plus space 4 space straight b with rightwards arrow on top space equals space minus 13 over 5 straight b with rightwards arrow on top
    therefore space space space straight c with rightwards arrow on top space and space straight b with rightwards arrow on top space have space opposite space directions. space
    Also,                open vertical bar straight c with rightwards arrow on top close vertical bar space equals space 13 over 5 open vertical bar straight b with rightwards arrow on top close vertical bar space space space space space space space space space space rightwards double arrow space space space space space space space open vertical bar straight c with rightwards arrow on top close vertical bar space greater than space open vertical bar straight b with rightwards arrow on top close vertical bar.

    Question 292
    CBSEENMA12033968

    Show that the line joining the middle points of the consecutive sides of a quadrilateral is a parallelogram.

    Solution
    Let P, Q, R, S be the mid-points of the sides AB, BC, CD, DA respectively of quadrilateral ABCD.

    therefore space space space PQ with rightwards arrow on top space equals space PB with rightwards arrow on top space plus space BQ with rightwards arrow on top space equals space 1 half space AB with rightwards arrow on top space plus space 1 half BC with rightwards arrow on top space equals space 1 half open parentheses AB with rightwards arrow on top plus BC with rightwards arrow on top close parentheses
    therefore space space space space PQ with rightwards arrow on top space equals space 1 half AC with rightwards arrow on top                                                       ...(1)
    Again, SR with rightwards arrow on top space equals SD with rightwards arrow on top space plus space DR with rightwards arrow on top space equals space 1 half AD with rightwards arrow on top space plus space 1 half DC with rightwards arrow on top space equals space 1 half open parentheses AD with rightwards arrow on top space plus space DC with rightwards arrow on top close parentheses
    therefore space space space space space space space space space SR with rightwards arrow on top space equals space 1 half space AC with rightwards arrow on top                                                  ...(2)
    From (1) and (2), we get
                                PQ with rightwards arrow on top space equals space SR with rightwards arrow on top

    ∴    sides PQ and SR are equal and parallel.
    Similarly sides PS and QR are equal and parallel.
    ∴   PQRS is a parallelogram.


    Question 293
    CBSEENMA12033969

    In the figure, M is the mid-point of AB and N is the mid-point of CD and O is the mid-point of MN. Prove that
    (i) OA with rightwards arrow on top space plus space OB with rightwards arrow on top space plus space OC with rightwards arrow on top space plus space OD with rightwards arrow on top space equals space straight O with rightwards arrow on top
    (ii) BC with rightwards arrow on top space plus space AD with rightwards arrow on top space equals space 2 space MN with rightwards arrow on top

    Solution

    We have
                              OA with rightwards arrow on top space plus space AM with rightwards arrow on top space equals space OM with rightwards arrow on top                             ...(1)
    and                   OB with rightwards arrow on top space plus space BM with rightwards arrow on top space equals space OM with bar on top                               ...(2)
    Adding (1) and (2) we get,
               OA with rightwards arrow on top space plus space OB with rightwards arrow on top space plus space AM with rightwards arrow on top space plus space BM with rightwards arrow on top space equals space 2 space OM with rightwards arrow on top
OA with rightwards arrow on top space plus OB with rightwards arrow on top space plus space AM with rightwards arrow on top space minus space AM with rightwards arrow on top space equals space 2 space OM with rightwards arrow on top space space space left square bracket because space space AM with rightwards arrow on top space equals space minus BM with rightwards arrow on top right square bracket
therefore space space space space space space space space OA with rightwards arrow on top space plus space OB with rightwards arrow on top space equals space 2 space OM with rightwards arrow on top space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 3 right parenthesis
Similarly space space space space OC with rightwards arrow on top space plus space OD with rightwards arrow on top space equals space 2 space ON with rightwards arrow on top space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 4 right parenthesis space space space space space space space space space space space space space space space space space space space space space space
    Adding (3) and (4), we get,
                   OA with rightwards arrow on top plus OB with rightwards arrow on top plus OC with rightwards arrow on top plus OD with rightwards arrow on top space equals space 2 space open parentheses OM with rightwards arrow on top plus ON with rightwards arrow on top close parentheses
                                                      equals space 2 space left parenthesis OM with rightwards arrow on top space minus space OM with rightwards arrow on top right parenthesis            open square brackets because space space space OM with rightwards arrow on top space equals space minus ON with rightwards arrow on top close square brackets
                                                       equals space 2 space left parenthesis 0 with rightwards arrow on top right parenthesis
             therefore space space space space OA with rightwards arrow on top space plus space OB with rightwards arrow on top space plus OC with rightwards arrow on top space plus space OD with rightwards arrow on top space equals space 0 with rightwards arrow on top
    Also,     BC with rightwards arrow on top space equals space BM with rightwards arrow on top space plus space MN with rightwards arrow on top space plus space NC with rightwards arrow on top space
    and       AD with rightwards arrow on top space equals space AM with rightwards arrow on top space plus space MN with rightwards arrow on top space plus space ND with rightwards arrow on top
    Adding,                    BC with rightwards arrow on top space plus space AD with rightwards arrow on top space equals space left parenthesis BM with rightwards arrow on top space plus space AM with rightwards arrow on top right parenthesis space plus space 2 space MN with rightwards arrow on top space plus space left parenthesis NC with rightwards arrow on top space plus space ND with rightwards arrow on top right parenthesis
                                                      equals space open parentheses negative AM with rightwards arrow on top space plus space AM with rightwards arrow on top close parentheses space plus space 2 space MN with rightwards arrow on top space plus left parenthesis space stack NC space with rightwards arrow on top space minus space NC with rightwards arrow on top right parenthesis
                  therefore space space space space space space space space BC with rightwards arrow on top space plus space AD with rightwards arrow on top space equals space 0 with rightwards arrow on top space plus space 2 space MN with rightwards arrow on top space plus space 0 with rightwards arrow on top
                                         equals 2 space MN with rightwards arrow on top
                

    Question 294
    CBSEENMA12033970

    Prove by vector method that the line segment joining the mid-points of the diagonals of trapezium is parallel to the parallel sides and equal to help of there difference.

    Solution
    Let ABCD be a trapezium and straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top space straight d with rightwards arrow on top be the position vectors of A, B, C, D respectively. Let P be the mid-point of diagonal AC and Q be mid-point of diagonal BD.
    therefore  position vectors of straight P with rightwards arrow on top space straight Q with rightwards arrow on top space are space fraction numerator straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top over denominator 2 end fraction comma space fraction numerator straight b with rightwards arrow on top space plus space straight d with rightwards arrow on top over denominator 2 end fraction respectively
                       PQ with rightwards arrow on top space space equals straight P. straight V. space of space straight Q space minus space straight P. straight V. space of space straight P
                                      equals space fraction numerator straight b with rightwards arrow on top space plus space straight d with rightwards arrow on top over denominator 2 end fraction space minus fraction numerator straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top over denominator 2 end fraction space equals space 1 half left parenthesis straight b with rightwards arrow on top space plus space straight d with rightwards arrow on top space minus space straight a with rightwards arrow on top space minus space straight c with rightwards arrow on top right parenthesis
equals space 1 half open square brackets left parenthesis straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top right parenthesis space minus space left parenthesis straight c with rightwards arrow on top space minus space stack straight d right parenthesis with rightwards arrow on top close square brackets
equals space 1 half open square brackets AB with rightwards arrow on top space minus space DC with rightwards arrow on top close square brackets

    Now,        AB || DC         rightwards double arrow space space space space space AB with rightwards arrow on top space equals space straight lambda. space DC with rightwards arrow on top
    therefore space space space space PQ with rightwards arrow on top space equals space 1 half open square brackets straight lambda. space stack DC space with rightwards arrow on top space minus space DC with rightwards arrow on top close square brackets space equals space 1 half left parenthesis straight lambda minus 1 right parenthesis space DC with rightwards arrow on top
therefore space space space PQ thin space vertical line vertical line thin space DC space space or space space space AB.
therefore space space space PQ space is space parallel space to space the space parallel space sides.
    Again,    open vertical bar AB with rightwards arrow on top close vertical bar space minus space open vertical bar DC with rightwards arrow on top close vertical bar space equals space straight lambda space open vertical bar DC with rightwards arrow on top close vertical bar space minus space open vertical bar DC close vertical bar space equals space left parenthesis straight lambda minus 1 right parenthesis thin space DC with rightwards arrow on top
    Now,  PQ with rightwards arrow on top space equals space 1 half left parenthesis straight lambda minus 1 right parenthesis space DC with rightwards arrow on top space space space rightwards double arrow space space space space space open vertical bar PQ with rightwards arrow on top close vertical bar space equals space 1 half left parenthesis straight lambda minus 1 right parenthesis space open vertical bar DC with rightwards arrow on top close vertical bar
    rightwards double arrow space space space space space open vertical bar PQ with rightwards arrow on top close vertical bar space equals space 1 half open parentheses open vertical bar AB with rightwards arrow on top close vertical bar space minus space open vertical bar DC with rightwards arrow on top close vertical bar close parentheses
    ∴   PQ is half of the difference of parallel sides.
    Hence the result.
    Question 295
    CBSEENMA12033971

    ABCD is a parallelogram. If L and M are the mid-point of BC and DC respectively, then express AL with rightwards arrow on top space and space AM with rightwards arrow on top in terms of AB with rightwards arrow on top space and space AD with rightwards arrow on top.

    Solution

    Take A as the origin. Let straight b with rightwards arrow on top space comma space straight d with rightwards arrow on top be position vectors of B and D respectively such that
        AB with rightwards arrow on top space equals space straight b with rightwards arrow on top space AD with rightwards arrow on top space equals space straight d with rightwards arrow on top
    Now,    AL with rightwards arrow on top space equals space AB with rightwards arrow on top space plus space BL with rightwards arrow on top
                      equals space AB with rightwards arrow on top space plus space 1 half BC with rightwards arrow on top
equals space AB with rightwards arrow on top space plus space 1 half AD with rightwards arrow on top space equals space straight b plus fraction numerator straight d with rightwards arrow on top over denominator 2 end fraction
therefore space space space space space space space position space vector space of space straight L space is space straight b with rightwards arrow on top space plus space fraction numerator straight d with rightwards arrow on top over denominator 2 end fraction
    Again AM with rightwards arrow on top space equals space AD with rightwards arrow on top space plus space DM with rightwards arrow on top space equals space AD with rightwards arrow on top space plus space 1 half space DC with rightwards arrow on top space equals space AD with rightwards arrow on top space plus space 1 half AB with rightwards arrow on top
                                     equals space straight d with rightwards arrow on top space plus space 1 half space straight b with rightwards arrow on top

    AC with rightwards arrow on top space equals space AB with rightwards arrow on top space plus space BC with rightwards arrow on top space equals space AB with rightwards arrow on top space plus space AD with rightwards arrow on top space equals space straight b with rightwards arrow on top space plus space straight d with rightwards arrow on top
                                 ...(1)
    AL with rightwards arrow on top space plus space AM with rightwards arrow on top space equals space open parentheses straight b with rightwards arrow on top space plus space fraction numerator straight d with rightwards arrow on top over denominator 2 end fraction close parentheses space plus space open parentheses straight d with rightwards arrow on top space plus space fraction numerator straight b with rightwards arrow on top over denominator 2 end fraction close parentheses space equals space 3 over 2 straight b with rightwards arrow on top space plus space 3 over 2 straight d with rightwards arrow on top
space space space space space space space space space space space space space space space space space space equals space 3 over 2 left parenthesis straight b with rightwards arrow on top space plus space straight d with rightwards arrow on top right parenthesis space equals space 3 over 2 AC with rightwards arrow on top space space space space space space space space space space space space space space space space space space left square bracket because space of space left parenthesis 1 right parenthesis right square bracket

    Question 296
    CBSEENMA12033972

    ABCDEF is a regular hexagon. Show that
    (i)  AB with rightwards arrow on top space plus space AC with rightwards arrow on top space plus space AD with rightwards arrow on top space plus space AE with rightwards arrow on top space plus space AF with rightwards arrow on top space equals space 3 space AD with rightwards arrow on top
    (ii) AB with rightwards arrow on top space plus space AC with rightwards arrow on top space plus space AD with rightwards arrow on top space plus space AE with rightwards arrow on top space plus space AF with rightwards arrow on top space equals space 6 space AO with rightwards arrow on top
    where O is centre of the hexagon.

    Solution

    ∵  O is centrc of regular hexagon
    ∵  O is the mid-point of each of the diagonals AD. BE. CF
    In ∆ ABE, O is mid-point of BE
    therefore space space space space AB with rightwards arrow on top space plus space AE with rightwards arrow on top space equals space 2 space AO with rightwards arrow on top                                  ...(1)
    In increment ACF comma   O is the mid-point of FC
    therefore space space space space space space AF with rightwards arrow on top space plus space AC with rightwards arrow on top space equals space 2 space AO with rightwards arrow on top                                 ...(2)
    Also,  AD with rightwards arrow on top space equals space 2 space AO with rightwards arrow on top                                           ...(3)
    as O is the mid-point of AD.

    Adding (1), (2) and (3), we get,
                             AB with rightwards arrow on top space plus space AC with rightwards arrow on top plus space AD with rightwards arrow on top space plus space AE with rightwards arrow on top space plus space AF with rightwards arrow on top space equals space 6 space AO with rightwards arrow on top
    therefore space space space space space space AB with rightwards arrow on top space plus space AC with rightwards arrow on top space plus space AD with rightwards arrow on top space plus space AE with rightwards arrow on top space plus space AF with rightwards arrow on top space equals 3 space AD with rightwards arrow on top

    Question 297
    CBSEENMA12033973

    Prove that the sum of all the v ectors from the centre of a regular octagon to its vertices is the zero vector.

    Solution

    Let O be the centre of regular octagon  ABCDEFGH.
               therefore        O is mid-point of each of the diagonals AE, BF, CG and DH.
    because                 O is mid-point of AE.
               because          OA with rightwards arrow on top space equals space minus OE with rightwards arrow on top
                therefore space space space OA with rightwards arrow on top space plus space OE with rightwards arrow on top space equals space 0 with rightwards arrow on top                          ...(1)

    Similarly OB with rightwards arrow on top space plus space OF with rightwards arrow on top space equals space 0 with rightwards arrow on top                                                                  ...(2)
    OC with rightwards arrow on top space plus space OG with rightwards arrow on top space equals space 0 with rightwards arrow on top                                             ...(3)
    OD with rightwards arrow on top space plus space OH with rightwards arrow on top space equals space 0 with rightwards arrow on top                                             ...(4)
    Adding (1), (2), (3) and (4). we get,
    OA with rightwards arrow on top space plus space OB with rightwards arrow on top space plus space OC with rightwards arrow on top space plus space OD with rightwards arrow on top space plus space OE with rightwards arrow on top space plus space OF with rightwards arrow on top space plus space OG with rightwards arrow on top space plus space OH with rightwards arrow on top space equals space 0 with rightwards arrow on top.
    Hence the result.
                     

    Question 298
    CBSEENMA12033974

    Show that the sum of three vector determined by the medians of a triangle directed from the vertices is zero.

    Solution
    Let D. E. F be the mid-points of the sides BC, CA and AB respectively of ∆ ABC
    Now,          AD with rightwards arrow on top space equals space AB with rightwards arrow on top space plus space BD with rightwards arrow on top                                    [Triangle Law of Vectors]
    therefore space space space space AD with rightwards arrow on top space equals space AB with rightwards arrow on top space plus space 1 half BC with rightwards arrow on top                          ...(1)
    Again,  BE with rightwards arrow on top space equals space BC with rightwards arrow on top space plus space CE with rightwards arrow on top
    therefore space space space space space BE with rightwards arrow on top space plus space BC with rightwards arrow on top space plus space 1 half CA with rightwards arrow on top                         ...(2)
    Also,    CF with rightwards arrow on top space equals CA with rightwards arrow on top space plus space AF with rightwards arrow on top
    therefore space space space space CF with rightwards arrow on top space equals space CA with rightwards arrow on top space plus space 1 half AB with rightwards arrow on top                           ...(3)

    Adding (1), (2) and (3),
    AD with rightwards arrow on top space plus space BE with rightwards arrow on top space plus space CF with rightwards arrow on top space equals space AB with rightwards arrow on top space plus space 1 half BC with rightwards arrow on top space plus space BC with rightwards arrow on top space plus space 1 half CA with rightwards arrow on top space plus space CA with rightwards arrow on top space plus space 1 half AB with rightwards arrow on top
                                             equals space 3 over 2 open square brackets AB with rightwards arrow on top space plus space BC with rightwards arrow on top space plus CA with rightwards arrow on top close square brackets
equals space 3 over 2 open square brackets AC with rightwards arrow on top space plus space CA with rightwards arrow on top close square brackets space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space space space AB with rightwards arrow on top plus BC with rightwards arrow on top space equals space AC with rightwards arrow on top close square brackets
equals space 3 over 2 open square brackets stack AC space with rightwards arrow on top space minus space AC with rightwards arrow on top close square brackets space equals space 3 over 2 open square brackets 0 with rightwards arrow on top close square brackets space equals space 0 with rightwards arrow on top
therefore space space space AD with rightwards arrow on top space plus space BE with rightwards arrow on top space plus space CF with rightwards arrow on top space equals space 0 with rightwards arrow on top
    Hence the result.
    Question 299
    CBSEENMA12033975

    Find the sum of the vectors
    straight a with rightwards arrow on top space equals space straight i with hat on top space minus space 2 straight j with hat on top space plus straight k with hat on top comma space space straight b with rightwards arrow on top space equals space minus 2 straight i with hat on top space plus space 4 straight j with hat on top space plus space 5 straight k with hat on top comma space straight c with rightwards arrow on top space equals space straight i with hat on top space minus space 6 straight j with hat on top space minus space 7 straight k with hat on top

    Solution

     straight a with rightwards arrow on top space equals space straight i with hat on top space minus space 2 straight j with hat on top space plus space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space minus 2 straight i with hat on top space plus space 4 straight j with hat on top space plus space 5 straight k with hat on top comma space space straight c with rightwards arrow on top space equals space straight i with hat on top space minus space 6 straight j with hat on top space minus space 7 straight k with hat on top
     Required vectors = straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top

                   equals space left parenthesis straight i with hat on top space minus space 2 space straight j with hat on top space plus space straight k with hat on top right parenthesis space plus space left parenthesis negative 2 space straight i with hat on top space plus space 4 space straight j with hat on top space plus space 5 space straight k with hat on top right parenthesis space plus space left parenthesis straight i with hat on top space minus space 6 space straight j with hat on top space minus space 7 space straight k with hat on top right parenthesis
equals space left parenthesis 1 minus 2 plus 1 right parenthesis space straight i with hat on top space plus space left parenthesis negative 2 plus 4 minus 6 right parenthesis space straight j with hat on top space plus space left parenthesis 1 plus 5 minus 7 right parenthesis space straight k with hat on top
equals space 0 space straight i with hat on top space minus space 4 space straight j with hat on top space minus space straight k with hat on top space equals space minus 4 space straight j with hat on top space minus space straight k with hat on top
    Question 300
    CBSEENMA12033976

    Compute the magnitude of the following vectors:
    straight a with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top space space semicolon space space space straight b with rightwards arrow on top space equals space 2 straight i with hat on top space minus space 7 straight j with hat on top space minus space 3 straight k with hat on top semicolon space space straight c with rightwards arrow on top space equals space fraction numerator 1 over denominator square root of 3 end fraction straight i with hat on top space plus space fraction numerator 1 over denominator square root of 3 end fraction straight j with hat on top space minus space fraction numerator 1 over denominator square root of 3 end fraction straight k with hat on top

    Solution

           straight a with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top
    therefore space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space square root of left parenthesis 1 right parenthesis squared plus left parenthesis 1 right parenthesis squared plus left parenthesis 1 right parenthesis squared end root space equals space square root of 1 plus 1 plus 1 end root space equals square root of 3
space space space space space space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space 7 space straight j with hat on top space minus space 3 space straight k with hat on top
therefore space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space square root of left parenthesis 2 right parenthesis squared plus left parenthesis negative 7 right parenthesis squared plus left parenthesis negative 3 right parenthesis squared end root space equals space square root of 4 plus 49 plus 9 end root space equals space square root of 62
            straight c with rightwards arrow on top space equals space fraction numerator 1 over denominator square root of 3 end fraction straight i with hat on top space plus space fraction numerator 1 over denominator square root of 3 end fraction straight j with hat on top space minus space fraction numerator 1 over denominator square root of 3 end fraction straight k with hat on top
    therefore space space space space space space open vertical bar straight c with rightwards arrow on top close vertical bar space equals space square root of open parentheses fraction numerator 1 over denominator square root of 3 end fraction close parentheses squared plus open parentheses fraction numerator 1 over denominator square root of 3 end fraction close parentheses squared plus open parentheses negative fraction numerator 1 over denominator square root of 3 end fraction close parentheses squared end root space equals space square root of 1 third plus 1 third plus 1 third end root equals space square root of 1 space equals 1

    Question 301
    CBSEENMA12033977

    Write two different vectors having same magnitude.

    Solution

    Let straight a with rightwards arrow on top space equals straight i with hat on top space plus space 2 space straight j with hat on top space plus space 2 space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space straight j with hat on top space plus space 2 space straight k with hat on top
    therefore space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space square root of left parenthesis 1 right parenthesis squared plus left parenthesis 2 right parenthesis squared plus left parenthesis 2 right parenthesis squared end root space equals space square root of 1 plus 4 plus 4 end root space equals square root of 9 space equals space 3
space space space space space space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space square root of left parenthesis 2 right parenthesis squared plus left parenthesis 1 right parenthesis squared plus left parenthesis 2 right parenthesis squared end root space equals square root of 4 plus 1 plus 4 end root space equals square root of 9 space equals 3
therefore space space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space open vertical bar straight b with rightwards arrow on top close vertical bar comma space space space but space straight a with rightwards arrow on top space not equal to space straight b with rightwards arrow on top
    as their corresponding components are not equal.

    Question 302
    CBSEENMA12033978

    Write two different vector having same direction.

    Solution

    Let straight a with rightwards arrow on top space equals space straight i with hat on top plus straight j with hat on top plus straight k with hat on top comma space space space space straight b with rightwards arrow on top space equals space 3 space straight i with hat on top space plus space 3 space straight j with hat on top space plus space 3 space straight k with hat on top
    Direction ratios of  straight a with rightwards arrow on top are 1, 1, 1 and direction ratios of straight b with rightwards arrow on top are 3, 3, 3.
     ∴   direction cosines of straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are 
                     fraction numerator 1 over denominator square root of 1 plus 1 plus 1 end root end fraction comma space fraction numerator 1 over denominator square root of 1 plus 1 plus 1 end root end fraction comma space fraction numerator 1 over denominator square root of 1 plus 1 plus 1 end root end fraction
    and  fraction numerator 3 over denominator square root of 9 plus 9 plus 9 end root end fraction comma space fraction numerator 3 over denominator square root of 9 plus 9 plus 9 end root end fraction comma space fraction numerator 3 over denominator square root of 9 plus 9 plus 9 end root end fraction space respectively.
    i.e. fraction numerator 1 over denominator square root of 3 end fraction comma space fraction numerator 1 over denominator square root of 3 end fraction comma space fraction numerator 1 over denominator square root of 3 end fraction space and space fraction numerator 1 over denominator square root of 3 end fraction comma space fraction numerator 1 over denominator square root of 3 end fraction comma space fraction numerator 1 over denominator square root of 3 end fraction
    therefore space space space straight a with rightwards arrow on top space and space straight b with rightwards arrow on top  are different vectors but have the same direction. 

    Question 303
    CBSEENMA12033979

    Find the values of x, y and z so that the vectorsstraight a with rightwards arrow on top space equals straight x space straight i with hat on top space plus space 2 space straight j with hat on top space plus space straight z space straight k with hat on top and  straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space straight y space straight j with hat on top space plus space straight k with hat on top are equal.

    Solution

    Here,   straight a with rightwards arrow on top space equals straight x space straight i with hat on top space plus space 2 space straight j with hat on top space plus space straight z space straight k with hat on top and straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space straight y space straight j with hat on top space plus space straight k with hat on top
    We know that two vectors are equal if and only if their corresponding components are equal
    therefore space space space space straight a with rightwards arrow on top space equals space straight b with rightwards arrow on top space space space space space space rightwards double arrow space space space space space space straight x space straight i with hat on top space plus space 2 space straight j with hat on top space plus space straight z space straight k with hat on top space equals space 2 space straight i with hat on top space plus space straight y space straight j with hat on top space plus space straight k with hat on top
rightwards double arrow space space space space space straight x space equals space 2 comma space space space straight y space equals space 2 comma space space straight z space equals space 1

    Question 304
    CBSEENMA12033980

    Find the magnitude of the vector straight a with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space 6 space straight j with hat on top space minus space 3 space straight k with hat on top.

    Solution
    straight a with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space 6 space straight j with hat on top space minus space 3 space straight k with hat on top
    therefore space space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space square root of left parenthesis 2 right parenthesis squared plus left parenthesis negative 6 right parenthesis squared plus left parenthesis negative 3 right parenthesis squared end root
                     equals space square root of 4 plus 36 plus 9 end root space equals space square root of 49 space equals space 7
    Question 305
    CBSEENMA12033981

    Find values of x for which straight x space open parentheses straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top close parentheses is a unit vector. 

    Solution

    Let straight a with rightwards arrow on top space equals space straight x space left parenthesis straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top right parenthesis space equals space straight x space straight i with hat on top space plus space straight x space straight j with hat on top space plus space straight x space straight k with hat on top
    Since straight a with rightwards arrow on top is a unit vector
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    Question 306
    CBSEENMA12033982

    Find the scalar and vector components of the vector with initial point (2, 1) and terminal point (– 5, 7).

    Solution
    Let P(2, 1) and Q(– 5, 7) be initial and terminal points.
    therefore space space space space PQ with rightwards arrow on top space equals space left parenthesis negative 5 minus 2 right parenthesis space straight i with hat on top space plus space left parenthesis 7 minus 1 right parenthesis space straight j with hat on top space equals space 7 space straight i with hat on top space plus space 6 space straight j with hat on top
    ∴    scalar components are – 7, 6 and vector components are negative 7 space straight i with hat on top comma space 6 space straight j with hat on top.
    Question 307
    CBSEENMA12033983

    Find the vector joining the points P(2, 3, 0) and Q (– 1, – 2,  – 4) directed from P to Q.

    Solution
    P(2, 3, 0), Q(– 1, – 2. – 4) are two given points
    therefore space space space space space space PQ with rightwards arrow on top space equals space left parenthesis negative 1 minus 2 right parenthesis space straight j with hat on top space plus space left parenthesis negative 2 minus 3 right parenthesis space straight j with hat on top space plus space left parenthesis negative 4 minus 0 right parenthesis space straight k with hat on top                                                                                       open square brackets because space space space PQ with rightwards arrow on top space equals space left parenthesis straight x subscript 2 minus straight x subscript 1 right parenthesis space straight i with hat on top space plus space left parenthesis straight y subscript 2 minus straight y subscript 1 right parenthesis space straight j with hat on top space plus space left parenthesis straight z subscript 2 minus straight z subscript 1 right parenthesis space straight k with hat on top close square brackets  
    i.e.,   PQ with rightwards arrow on top space equals space minus 3 straight i with hat on top space minus space 5 straight j with hat on top space minus space 4 straight k with hat on top.
    Question 308
    CBSEENMA12033984

    Find the unit vector in the direction of vector PQ with rightwards arrow on top, where P and Q are the points (1, 2, 3) and (4, 5, 6) respectively.

    Solution
    Given points are P (1. 2. 3), Q (4. 5, 6)

    therefore space space space space space PQ with rightwards arrow on top space equals space straight P. straight V. space of space straight Q space minus space straight P. straight V. space of space straight P
space space space space space space space space space space space space space space space space space equals space left parenthesis 4 straight i with hat on top space plus space space 5 straight j with hat on top space plus space 6 straight k with hat on top right parenthesis space minus left parenthesis straight i with hat on top plus 2 straight j with hat on top plus 3 straight k with hat on top right parenthesis space equals space 3 straight i with hat on top space plus space 3 straight j with hat on top space plus space 3 straight k with hat on top
therefore space space space space open vertical bar PQ with rightwards arrow on top close vertical bar space equals space square root of 9 plus 9 plus 9 end root space equals space square root of 27 space equals space square root of 9 space cross times 3 end root space equals space 3 square root of 3
    Unit vector in the direction of PQ is = fraction numerator PQ with rightwards arrow on top over denominator open vertical bar PQ with rightwards arrow on top close vertical bar end fraction
                                    equals space fraction numerator 1 over denominator 3 square root of 3 end fraction left parenthesis 3 straight i with hat on top space plus space 3 straight j with hat on top space plus space 3 space straight k with hat on top right parenthesis space equals space fraction numerator 1 over denominator square root of 3 end fraction straight i with hat on top space plus space fraction numerator 1 over denominator square root of 3 end fraction straight j with hat on top space plus fraction numerator 1 over denominator square root of 3 end fraction straight k with hat on top
    Question 309
    CBSEENMA12033985

    Find the direction cosines of the vector joining the points A (1, 2, – 3) and B (– 1, – 2. 1). directed from A to B.

    Solution

    A(1, 2, 3), B(-1, 2, 1) are given points. 
    therefore space space space space space AB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A
                        equals left parenthesis negative straight i with hat on top space minus space 2 space straight j with hat on top space plus space straight k with hat on top right parenthesis space minus space left parenthesis straight i with hat on top space plus space 2 space straight i with hat on top space minus space 3 straight k with hat on top right parenthesis
    therefore space space space space space space space open vertical bar AB with rightwards arrow on top close vertical bar space equals space minus 2 straight i with hat on top space minus space 4 straight j with hat on top space plus space 4 straight k with hat on top
therefore space space space space space space open vertical bar AB with rightwards arrow on top close vertical bar space equals space minus 2 straight i with hat on top space minus space 4 space straight j with hat on top space plus space 4 space straight k with hat on top
therefore space space space space space open vertical bar AB with rightwards arrow on top close vertical bar space equals space square root of left parenthesis negative 2 right parenthesis squared plus left parenthesis negative 4 right parenthesis squared plus left parenthesis 4 right parenthesis squared end root space equals space square root of 4 plus 16 plus 16 end root space equals square root of 36 space equals 6
therefore space space space space unit space vector space along space AB with rightwards arrow on top
space space space space space space space space space space space space space space space space space space equals space fraction numerator AB with rightwards arrow on top over denominator open vertical bar AB with rightwards arrow on top close vertical bar end fraction space equals 1 over 6 left parenthesis negative 2 space straight i with hat on top space minus space 4 space straight j with hat on top space plus space 4 space straight k with hat on top right parenthesis
space space space space space space space space space space space space space space space space space space equals space minus 1 third straight i with hat on top space minus space 2 over 3 straight j with hat on top space plus space 2 over 3 straight k with hat on top
therefore space space space space space required space direction space cosines space are space space minus 1 third comma space minus 2 over 3 comma space 2 over 3.

    Question 310
    CBSEENMA12033986

    If A is (a1 , a2 , a3), AB with rightwards arrow on top is vector straight b with rightwards arrow on top space equals space straight b subscript 1 straight i with hat on top space plus space straight b subscript 2 straight j with hat on top space plus space straight b subscript 3 straight k with hat on top, find the coordinates of B.

    Solution

    Here straight A space equals space left parenthesis straight a subscript 1 comma space straight a subscript 2 comma space straight a subscript 3 right parenthesis space space rightwards double arrow space space space space space space straight P. straight V. space space of space straight A space equals space straight a subscript 1 straight i with hat on top space plus space straight a subscript 2 straight j with hat on top space plus space straight a subscript 3 straight k with hat on top
          Let B be left parenthesis straight lambda subscript 1 comma space straight lambda subscript 2 comma space straight lambda subscript 3 right parenthesis
    therefore space space space space space straight P. straight V. space of space straight B space equals space straight lambda subscript 1 straight i with hat on top space plus space straight lambda subscript 2 straight j with hat on top space plus space straight lambda subscript 3 straight k with hat on top
    Now,   AB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A
    rightwards double arrow space space space straight b with rightwards arrow on top space equals space left parenthesis straight lambda subscript 1 straight i with hat on top space plus space straight lambda subscript 2 straight j with hat on top space plus space straight lambda subscript 3 straight k with hat on top right parenthesis space minus space left parenthesis straight a subscript 1 straight i with hat on top space plus space straight a subscript 2 straight j with hat on top space plus space straight a subscript 3 straight k with hat on top right parenthesis
rightwards double arrow space space space straight b subscript 1 straight i with hat on top space plus space straight b subscript 2 straight j with hat on top space plus space straight b subscript 3 straight k with hat on top space equals space left parenthesis straight lambda subscript 1 minus straight a subscript 1 right parenthesis space straight i with hat on top space plus space left parenthesis straight lambda subscript 2 minus straight a subscript 2 right parenthesis space straight j with hat on top space plus space left parenthesis straight lambda subscript 3 minus straight a subscript 3 right parenthesis space straight k with hat on top
rightwards double arrow space space space straight lambda subscript 1 minus straight a subscript 1 space equals space straight b subscript 1 comma space straight lambda subscript 2 minus straight a subscript 2 space equals space straight b subscript 2 comma space space space space straight lambda subscript 3 minus straight a subscript 3 space equals space straight b subscript 3
rightwards double arrow space space space space straight lambda subscript 1 space equals space straight a subscript 1 space plus space straight b subscript 1 comma space space straight lambda subscript 2 space equals space straight a subscript 2 space plus space straight b subscript 2 comma space space straight lambda subscript 3 space equals space straight a subscript 3 space plus space straight b subscript 3
therefore space space space straight B space is space left parenthesis straight a subscript 1 plus straight b subscript 1 comma space straight a subscript 2 plus straight b subscript 2 comma space straight a subscript 3 plus straight b subscript 3 right parenthesis.

    Question 311
    CBSEENMA12033987

    If PQ with rightwards arrow on top space equals space 3 straight i with hat on top space plus space 2 straight j with hat on top space minus space straight k with hat on top and the coordinates of P are (1, – 1, – 2), find the coordinates of Q.

    Solution

    Here P = (1, -1, -2)    rightwards double arrow   P.V. of P = straight i with hat on top space minus space straight j with hat on top space minus space 2 straight k with hat on top
    Let Q be left parenthesis straight lambda subscript 1 comma space straight lambda subscript 2 comma space straight lambda subscript 3 right parenthesis
    therefore space space space space straight P. straight V. space of space straight Q space equals space straight lambda subscript 1 straight i with hat on top space space plus space straight lambda subscript 2 straight j with hat on top space plus space straight lambda subscript 3 straight k with hat on top
    Now,  PQ with rightwards arrow on top space equals space straight P. straight V. space of space straight Q space minus space straight P. straight V. space of space straight P
    rightwards double arrow space space space space space 3 straight i with hat on top plus space 2 straight j with hat on top space minus space straight k with hat on top space equals space left parenthesis straight lambda subscript 1 straight i with hat on top space plus space straight lambda subscript 2 straight j with hat on top space plus space straight lambda subscript 3 straight k with hat on top right parenthesis space minus space left parenthesis straight i with hat on top space minus space straight j with hat on top space minus space 2 space straight k with hat on top right parenthesis
rightwards double arrow space space space space 3 space straight i with hat on top space plus space 2 space straight j with hat on top space minus space straight k with hat on top space equals space left parenthesis straight lambda subscript 1 space minus space 1 right parenthesis straight i with hat on top space plus space left parenthesis straight lambda subscript 2 space plus space 1 right parenthesis space straight j with hat on top space plus space left parenthesis straight lambda subscript 3 space plus 2 right parenthesis space straight k with hat on top
rightwards double arrow space space space 3 space equals space straight lambda subscript 1 space minus space 1 comma space space 2 space equals space straight lambda subscript 2 plus 1 comma space space minus 1 space equals space straight lambda subscript 3 plus 2
rightwards double arrow space space space straight lambda subscript 1 space equals space 4 comma space space space space space straight lambda subscript 2 space equals space 1 comma space space space straight lambda subscript 3 space equals space minus 3 comma
therefore space space space space straight Q space is space left parenthesis 4 comma space 1 comma space minus 3 right parenthesis.

    Question 312
    CBSEENMA12033988

    Find the values of x and y so that the vectors 2 straight i with hat on top space plus space 3 straight j with hat on top and straight x straight i with hat on top space plus space straight y straight j with hat on top are equal.

    Solution

    Since 2 straight i with hat on top plus space 3 straight j with hat on top and straight x straight i with hat on top space plus space straight y straight j with hat on top are equal
    therefore their corresponding components are equal
    therefore space space space space straight x space equals space 2 comma space space space straight y space equals space 3.

    Question 313
    CBSEENMA12033989

    Let straight a with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top and straight b with rightwards arrow on top space equals space 2 straight i with hat on top space plus space straight j with hat on top. Is open vertical bar straight a with rightwards arrow on top close vertical bar space equals space open vertical bar straight b with rightwards arrow on top close vertical bar space ? Are the vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top equal?

    Solution
    straight a with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top comma space space space straight b with rightwards arrow on top space equals space 2 straight i with hat on top space plus space straight j with hat on top
                       open vertical bar straight a with rightwards arrow on top close vertical bar space equals space square root of left parenthesis 1 right parenthesis squared plus left parenthesis 2 right parenthesis squared end root space equals space square root of 1 plus 4 end root space equals space square root of 5
open vertical bar straight b with rightwards arrow on top close vertical bar space equals space square root of left parenthesis 2 right parenthesis squared plus left parenthesis 1 right parenthesis squared end root space equals space square root of 4 plus 1 end root space equals space square root of 5
    therefore space space space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space open vertical bar straight b with rightwards arrow on top close vertical bar
    straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are not equal as their corresponding components are distinct.
    Question 314
    CBSEENMA12033990

    Find a unit vector in the direction of straight a with rightwards arrow on top space equals space 3 space straight i with hat on top space minus space 2 space straight j with hat on top space plus space 6 space straight k with hat on top.

    Solution

         straight a with rightwards arrow on top space equals space 3 straight i with hat on top space minus space space 2 straight j with hat on top space plus space 6 straight k with hat on top
    therefore space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space square root of left parenthesis 3 right parenthesis squared plus left parenthesis negative 2 right parenthesis squared plus left parenthesis 6 right parenthesis squared end root space equals space square root of 9 plus 4 plus 36 end root space equals space square root of 49 space equals space 7
    therefore            unit vector in the direction of straight a with rightwards arrow on top
                                          equals space fraction numerator straight a with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top close vertical bar end fraction space equals space 1 over 7 left parenthesis 3 straight i with hat on top space minus space 2 straight j with hat on top space plus space 6 space straight k with hat on top right parenthesis
                                         equals space 3 over 7 straight i with hat on top space minus space 2 over 7 straight j with hat on top space plus space 6 over 7 straight k with hat on top.

    Question 315
    CBSEENMA12033991
    Question 316
    CBSEENMA12033992
    Question 317
    CBSEENMA12033993

    If straight a with rightwards arrow on top space equals space straight i with hat on top space plus space 2 straight j with hat on top space minus space straight k with hat on top space and space straight b with rightwards arrow on top space equals space 3 straight i with hat on top space plus space straight j with hat on top space minus space 5 space straight k with hat on top comma find a unit vector in the direction of straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top.

    Solution

    Here,          straight a with rightwards arrow on top space equals space straight i with hat on top space space plus space 2 straight j with hat on top space minus space straight k with hat on top comma space space straight b with rightwards arrow on top equals space 3 space straight i with hat on top space plus space straight j with hat on top space minus space 5 space straight k with hat on top
    therefore space space space space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space equals space left parenthesis straight i with hat on top space plus space 2 space straight j with hat on top space minus space straight k with hat on top right parenthesis space minus space left parenthesis 3 space straight i with hat on top space plus space straight j with hat on top space minus space 5 space straight k with hat on top right parenthesis space equals space minus 2 space straight i with hat on top space plus space straight j with hat on top space plus space 4 space straight k with hat on top
therefore space space space space space space open vertical bar straight a with rightwards arrow on top minus straight b with rightwards arrow on top close vertical bar space equals space square root of left parenthesis negative 2 right parenthesis squared plus left parenthesis 1 right parenthesis squared plus left parenthesis 4 right parenthesis squared end root space equals space square root of 4 plus 1 plus 16 end root space equals space square root of 21
therefore space space space space space unit space vector space in space the space direction space of space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top
                      equals space fraction numerator straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar end fraction space equals space fraction numerator 1 over denominator square root of 21 end fraction space left parenthesis negative 2 space straight i with hat on top space plus space straight j with hat on top space space plus space 4 space straight k with hat on top right parenthesis
equals space minus fraction numerator 2 over denominator square root of 21 end fraction straight i with hat on top space plus space fraction numerator 1 over denominator square root of 21 end fraction straight j with hat on top space plus space fraction numerator 4 over denominator square root of 21 end fraction straight k with hat on top.

    Question 318
    CBSEENMA12033994
    Question 319
    CBSEENMA12033995

    For given vectors, straight a with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space straight j with hat on top space plus space 2 space straight k with hat on top space and space straight b with rightwards arrow on top space equals space minus straight i with hat on top space plus space straight j with hat on top space minus space straight k with hat on top comma space find the unit vector in the direction of the vector straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top.

    Solution

    Here straight a with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space straight j with hat on top space plus space 2 space straight k with hat on top comma space space space space straight b with rightwards arrow on top space equals space minus straight i with hat on top space plus space straight j with hat on top space space minus space straight k with hat on top
    therefore space space space space space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space equals space straight i with hat on top space plus space straight k with hat on top
                     open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar space equals space square root of left parenthesis 1 right parenthesis squared plus left parenthesis 0 right parenthesis squared plus left parenthesis 1 right parenthesis squared end root space equals space square root of 1 plus 0 plus 1 end root space equals space square root of 2
    therefore space space space unit space vector space in space the space direction space of space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top
                                 equals space fraction numerator straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar end fraction space equals space fraction numerator 1 over denominator square root of 2 end fraction left parenthesis straight i with hat on top space plus space straight k with hat on top right parenthesis space equals space fraction numerator 1 over denominator square root of 2 end fraction straight i with hat on top space plus space fraction numerator 1 over denominator square root of 2 end fraction straight k with hat on top

    Question 320
    CBSEENMA12033996

    If straight a with rightwards arrow on top space equals straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top,    straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space straight j with hat on top space plus space 3 space straight k with hat on top and straight c with rightwards arrow on top space equals space straight i with hat on top space minus space 2 space straight j with hat on top space plus space straight k with hat on top, find a vector parallel to the vector 2 space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space plus space 3 space straight c with rightwards arrow on top.

    Solution

           straight a with rightwards arrow on top space equals space straight i with hat on top plus straight j with hat on top plus straight k with hat on top comma space space straight b with rightwards arrow on top space equals space 2 straight i with hat on top space minus space straight j with hat on top space space 3 straight k with hat on top comma space space straight c with rightwards arrow on top space equals space straight i with hat on top space minus space 2 space straight j with hat on top space plus space straight k with hat on top
    therefore space space space space 2 space straight a with rightwards arrow on top minus straight b with rightwards arrow on top space plus space 3 straight c with rightwards arrow on top space equals space 2 left parenthesis straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top right parenthesis space minus space left parenthesis 2 straight i with hat on top space minus space straight j with hat on top space plus space 3 space straight k with hat on top right parenthesis space plus space 3 left parenthesis straight i with hat on top space minus space 2 space straight j with hat on top space plus space straight k with hat on top right parenthesis
                                 equals space 2 straight i with hat on top space plus space 2 straight j with hat on top space plus space 2 space straight k with hat on top space minus space 2 straight i with hat on top space plus space straight j with hat on top space minus space 3 straight k with hat on top space plus space space 3 straight i with hat on top space minus space 6 straight j with hat on top space plus space 3 straight k with hat on top
space equals space 3 straight i with hat on top space minus space 3 straight j with hat on top space plus space 2 space straight k with hat on top
    therefore space space space space open vertical bar space 2 straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space plus space 3 straight c with rightwards arrow on top close vertical bar space equals space square root of left parenthesis 3 right parenthesis squared plus left parenthesis negative 3 right parenthesis squared plus left parenthesis 2 right parenthesis squared end root space equals square root of 9 plus 9 plus 4 end root space equals space square root of 22
therefore space space space space unit space vector space parallel space to space 2 straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space plus space space 3 space straight c with rightwards arrow on top
space space space space space space space space space space space space space space space space space space space space space space space space equals space fraction numerator 2 straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space plus space 3 straight c with rightwards arrow on top over denominator open vertical bar 2 space close vertical bar end fraction space equals fraction numerator 1 over denominator square root of 22 end fraction left parenthesis 2 straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space plus space 3 space straight c with rightwards arrow on top right parenthesis
space space space space space space space space space space space space space space space space space space space space space space space equals space fraction numerator 1 over denominator square root of 22 end fraction left parenthesis 3 space straight i with hat on top space minus space 3 space straight j with hat on top space space plus space 2 space straight k with hat on top right parenthesis space equals space fraction numerator 3 over denominator square root of 22 end fraction straight i with hat on top space minus space fraction numerator 3 over denominator square root of 22 end fraction straight j with hat on top space plus space fraction numerator 2 over denominator square root of 22 end fraction straight k with hat on top

    Question 321
    CBSEENMA12033997

    Find a vector in the direction of vector 5 space straight i with hat on top space minus space straight j with hat on top space plus space 2 space straight k with hat on top which has magnitude 8 units. 

    Solution

    Let straight a with rightwards arrow on top space equals space 5 straight i with hat on top space minus space straight j with hat on top space plus space 2 straight k with hat on top
          therefore space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space square root of left parenthesis 5 right parenthesis squared plus left parenthesis negative 1 right parenthesis squared plus left parenthesis 2 right parenthesis squared end root space equals space square root of 25 plus 1 plus 4 end root space equals space square root of 30
    Unit vector along straight a with rightwards arrow on top is 
                            equals space fraction numerator straight a with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top close vertical bar end fraction space equals space fraction numerator 1 over denominator square root of 30 end fraction left parenthesis 5 straight i with hat on top space minus space straight j with hat on top space plus space 2 straight k with hat on top right parenthesis
    Required vector = 8 space open parentheses fraction numerator straight a with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top close vertical bar end fraction close parentheses space equals space fraction numerator 8 over denominator square root of 30 end fraction left parenthesis 5 space straight i with hat on top space minus space straight j with hat on top space plus space 2 space straight k with hat on top right parenthesis
                             equals space fraction numerator 40 over denominator square root of 30 end fraction straight i with hat on top space minus space fraction numerator 8 over denominator square root of 30 end fraction straight j with hat on top space plus space fraction numerator 16 over denominator square root of 30 end fraction straight k with hat on top

    Question 322
    CBSEENMA12033998

    Find a vector of magnitude 5 units, and parallel to the resultant of the vectors 
    straight a with rightwards arrow on top space equals space 2 straight i with hat on top space plus space 3 straight j with hat on top space minus space straight k with hat on top space and space straight b with rightwards arrow on top space equals space straight i with hat on top space minus space 2 space straight j with hat on top space plus space straight k with hat on top.

    Solution

          straight a with rightwards arrow on top space equals space 2 straight i with hat on top plus 3 straight j with hat on top space minus straight k with hat on top comma space space space space space space space straight b with rightwards arrow on top space equals space straight i with hat on top space minus space 2 straight j with hat on top space plus space straight k with hat on top
    therefore space space space space space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space equals space 3 straight i with hat on top space plus space straight j with hat on top
therefore space space space space open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar space equals space square root of left parenthesis 3 right parenthesis squared plus left parenthesis 1 right parenthesis squared end root space equals space square root of 9 plus 1 end root space equals space square root of 10
therefore space space space straight a space unit space vector space parallel space to space straight a with rightwards arrow on top plus straight b with rightwards arrow on top space is space space equals space fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top space plus straight b with rightwards arrow on top close vertical bar end fraction space equals fraction numerator 1 over denominator square root of 10 end fraction left parenthesis 3 straight i with hat on top space plus space straight j with hat on top right parenthesis space equals space open parentheses fraction numerator 3 over denominator square root of 10 end fraction straight i with hat on top space plus space fraction numerator 1 over denominator square root of 10 end fraction straight j with hat on top close parentheses
    Required vector  = 5 open parentheses fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar end fraction close parentheses space equals space 5 space open parentheses fraction numerator 3 over denominator square root of 10 end fraction straight i with hat on top space plus space fraction numerator 1 over denominator square root of 10 end fraction straight j with hat on top close parentheses
                              equals space fraction numerator 15 over denominator square root of 10 end fraction straight i with hat on top space plus space fraction numerator 5 over denominator square root of 10 end fraction straight j with hat on top space equals space 3 over 2 square root of 10 space straight i with hat on top space plus space 1 half square root of 10 space straight j with hat on top

    Question 323
    CBSEENMA12033999

    Show that the vectors 2 space straight i with hat on top minus 3 space straight j with hat on top space plus 4 space straight k with hat on top and negative 4 space straight i with hat on top space plus space 6 space straight j with hat on top space minus space 8 space straight k with hat on top are collinear.

    Solution

    Let       straight a with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space space 3 space straight j with hat on top space plus space 4 space straight k with hat on top
    and      straight b with rightwards arrow on top space equals space minus 4 space straight i with hat on top space plus space 6 space straight j with hat on top space minus space 8 space straight k with hat on top space equals space minus 2 left parenthesis 2 space straight i with hat on top space minus space space 3 space straight j with hat on top space plus space 4 space straight k with hat on top right parenthesis
    therefore space space space space space straight b with rightwards arrow on top space equals space minus 2 straight a with rightwards arrow on top
rightwards double arrow space space space space space straight a with rightwards arrow on top space equals space fraction numerator negative space 1 over denominator 2 end fraction straight b with rightwards arrow on top
    therefore            straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are collinear.

    Question 324
    CBSEENMA12034000

    Find the condition that the vectors straight a with rightwards arrow on top space equals space straight k space straight i with hat on top space plus space straight l space straight j with hat on top space and space straight b with rightwards arrow on top space equals space straight l space straight i with hat on top space plus space straight k space straight j with hat on top comma space space left parenthesis straight k comma space straight l space not equal to 0 right parenthesis space are space parallel

    Solution

    Here,   straight a with rightwards arrow on top space equals space straight k space straight i with hat on top space plus space straight l space straight j with hat on top comma space space straight b with rightwards arrow on top space equals space straight l space straight i with hat on top space plus space straight k space straight j with hat on top
    Let straight a with rightwards arrow on top space and space straight b with rightwards arrow on top be parallel.
    therefore space  there exists a non-zero scalar straight lambda such that straight a with rightwards arrow on top space equals space straight lambda space straight b with rightwards arrow on top
    therefore space space space straight k space straight i with hat on top space plus space straight l space straight j with hat on top space equals space straight lambda space li with rightwards arrow on top space plus space λk straight j with rightwards arrow on top
therefore space space left parenthesis straight k minus straight lambda space straight l right parenthesis space straight i with hat on top space plus space left parenthesis straight l minus straight lambda space straight k right parenthesis space straight j with hat on top space equals space 0 with rightwards arrow on top
rightwards double arrow space space straight k space minus space straight lambda space straight l space equals space 0 comma space space space space straight l space minus straight lambda space straight k space equals space 0
rightwards double arrow space space space space straight lambda space equals space straight k over straight l comma space straight lambda space equals space straight l over straight k
    Equating values of straight lambda comma we get,
                             straight k over straight l space equals space straight l over straight k space space space or space space space straight k squared space equals space straight l squared
    which is required condition. 

    Question 325
    CBSEENMA12034001

    Prove that if straight u with rightwards arrow on top space equals space straight u subscript 1 space straight i with hat on top space plus space straight u subscript 2 space straight j with hat on top space and space straight v with rightwards arrow on top space equals space straight v subscript 1 space straight i with hat on top space plus space straight v subscript 2 space straight j with hat on top are non-zero vectors, then they are parallel if and only if u2v2 – u2v1 = 0.

    Solution

    Let straight u with rightwards arrow on top space equals space straight u subscript 1 straight i with hat on top space plus space straight u subscript 2 straight j with hat on top comma space space straight v with rightwards arrow on top space equals space straight v subscript 1 straight i with hat on top space plus space straight v subscript 2 straight j with hat on top be parallel vectors. 
    therefore space space space there space exists space straight a space non minus zero space scalar space straight k space such space that space straight u with rightwards arrow on top space equals space straight k space straight v with rightwards arrow on top
therefore space space space space straight u subscript 1 straight i with hat on top space plus space straight u subscript 2 straight j with hat on top space equals space straight k left parenthesis straight v straight i with hat on top space plus space straight v subscript 2 straight j with hat on top right parenthesis
or space space left parenthesis straight u subscript 1 space space minus space kv subscript 1 right parenthesis space equals space 0 comma space space space straight u subscript 2 space minus kv subscript 2 space equals space 0
therefore space space space space straight k space equals space straight u subscript 1 over straight v subscript 1 comma space space space straight k space equals space straight u subscript 2 over straight v subscript 2
Equating space values space of space straight k comma space we space get comma
space space space space space space space space space space space space space space space space space space space space straight u subscript 1 over straight v subscript 1 space equals space straight u subscript 2 over straight v subscript 2
therefore space space space space space space space space straight u subscript 1 straight v subscript 2 space equals space straight u subscript 2 straight v subscript 1 space space space space space space space space space rightwards double arrow space space space space space straight u subscript 1 straight v subscript 2 space minus space straight u subscript 2 space straight v subscript 1 space equals space 0
    Similarly, if straight u subscript 1 space straight v subscript 2 space equals space straight u subscript 2 space straight v subscript 1 space space space space rightwards double arrow space space space space space straight u subscript 1 space straight v subscript 2 space minus space straight u subscript 2 space straight v subscript 1 space equals space 0
    i.e.,       straight u with rightwards arrow on top comma space space straight v with rightwards arrow on top are parallel
    Hence the result.
       

    Question 326
    CBSEENMA12034002

    Find the condition that the vectors straight a with rightwards arrow on top space equals space straight k space straight i with hat on top space plus space 3 space straight j with hat on top space and space straight b with rightwards arrow on top space equals space 4 space straight i with hat on top space plus space straight k space straight j with hat on top comma space space left parenthesis straight k space not equal to space 0 right parenthesis are parallel.

    Solution

    Here,   straight a with rightwards arrow on top space equals space straight k straight i with hat on top space plus space 3 straight j with hat on top comma space space straight b with rightwards arrow on top space equals space 4 straight i with hat on top space plus space space straight k straight j with hat on top
    Let straight a with rightwards arrow on top space and space straight b with rightwards arrow on top   be parallel..
      therefore space space   there exists a non-zero scalar straight lambda such that
                   straight a with rightwards arrow on top space equals space straight lambda straight b with rightwards arrow on top
    therefore space space straight k space straight i with hat on top space plus space 3 space straight j with hat on top space equals space 4 space straight lambda space straight i with hat on top space plus space straight lambda space straight k space straight j with hat on top
therefore space space space left parenthesis straight k space minus space 4 space straight lambda right parenthesis space straight i with hat on top space plus space left parenthesis 3 space minus space straight k space straight lambda right parenthesis space straight j with hat on top space equals space 0 with rightwards arrow on top
rightwards double arrow space space space space straight k space minus space 4 space straight lambda space equals space 0 comma space space space space 3 space space minus space straight k space straight lambda space equals space 0
rightwards double arrow space space space space space space space space space space space space space straight lambda space equals straight k over 4 comma space space space space straight lambda space equals space 3 over straight k
    Equating values of straight lambda comma we get,
                          straight k over 4 space equals space 3 over straight k space space space or space space space straight k squared space equals space 4 space cross times space 3 space equals space 12
    which is required condition. 
                 

    Question 327
    CBSEENMA12034003

    If the sum of two unit vectors is a unit vector, show that the magnitude of their difference is square root of 3

    Solution

    Let straight a with rightwards arrow on top space equals space straight x subscript 1 straight i with hat on top space plus space straight y subscript 1 straight j with hat on top space plus space straight z subscript 1 straight k with hat on top comma space space straight b with rightwards arrow on top space equals space straight a with rightwards arrow on top space equals straight x subscript 2 straight i with hat on top space space plus space straight y subscript 2 space straight j with hat on top space plus space straight z subscript 2 straight k with hat on top  be two units vectors such that 
    straight a with rightwards arrow on top plus straight b with rightwards arrow on top is also a unit vector. 
    therefore space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 1 comma space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 1 comma space space space open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar space equals space 1
              open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 1 space space space space rightwards double arrow space space space space square root of straight x subscript 1 squared plus straight y subscript 1 squared plus straight z subscript 1 squared end root space equals space 1 space space space space space rightwards double arrow space space space space straight x subscript 1 squared plus space straight y subscript 1 squared plus straight z subscript 1 squared space equals space 1 space space space space space space... left parenthesis 1 right parenthesis
open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 1 space rightwards double arrow space space space square root of straight x subscript 2 squared plus straight y subscript 2 squared plus straight z subscript 2 squared end root space equals space 1 space space space space space space space space space space rightwards double arrow space space straight x subscript 2 squared plus straight y subscript 2 squared plus straight z subscript 2 squared space equals space 1 space space space space space space space space space space... left parenthesis 2 right parenthesis
open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar space equals space 1 space space rightwards double arrow space space space space square root of left parenthesis straight x subscript 1 plus straight x subscript 2 right parenthesis squared space plus space left parenthesis straight y subscript 1 plus straight y subscript 2 right parenthesis squared plus left parenthesis straight z subscript 1 plus straight z subscript 2 right parenthesis squared end root space equals space 1
    rightwards double arrow space space space space space left parenthesis straight x subscript 1 plus straight x subscript 2 right parenthesis squared plus space left parenthesis straight y subscript 1 plus straight y subscript 2 right parenthesis squared space plus space left parenthesis straight z subscript 1 plus straight z subscript 2 right parenthesis squared space equals space 1
rightwards double arrow space space space space left parenthesis straight x subscript 1 squared plus straight y subscript 1 squared plus straight z subscript 1 squared right parenthesis space plus space left parenthesis straight x subscript 2 squared plus straight y subscript 2 squared plus straight z subscript 2 squared right parenthesis space plus space 2 left parenthesis straight x subscript 1 straight x subscript 2 plus straight y subscript 1 straight y subscript 2 plus straight y subscript 1 plus straight z subscript 1 straight z subscript 2 right parenthesis space equals 1
rightwards double arrow space space space 1 plus 1 plus 2 space left parenthesis straight x subscript 1 straight x subscript 2 space plus space straight y subscript 1 straight y subscript 2 plus straight z subscript 1 straight z subscript 2 right parenthesis space equals space minus 1 space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 3 right parenthesis
Now comma space open vertical bar straight a with rightwards arrow on top minus space straight b with rightwards arrow on top close vertical bar space equals space square root of left parenthesis straight x subscript 1 minus straight x subscript 2 right parenthesis squared plus left parenthesis straight y subscript 1 minus straight y subscript 2 right parenthesis squared plus left parenthesis straight z subscript 1 minus straight z subscript 2 right parenthesis squared end root
space space space space equals space square root of left parenthesis straight x subscript 1 squared plus straight y subscript 1 squared plus straight y subscript 1 squared right parenthesis space plus space left parenthesis straight x subscript 2 squared plus straight y subscript 2 squared plus straight z subscript 2 squared right parenthesis space minus space 2 left parenthesis straight x subscript 1 straight x subscript 2 plus straight y subscript 1 straight y subscript 2 plus straight z subscript 1 straight z subscript space 2 end subscript right parenthesis end root
space space space space equals space square root of 1 plus 1 plus 1 end root space equals space square root of 3 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space left square bracket because space of space left parenthesis 1 right parenthesis comma space left parenthesis 2 right parenthesis comma space left parenthesis 3 right parenthesis right square bracket space space space space space space space space space space space space space space space space space space space space space space space space space space space

    Question 328
    CBSEENMA12034004

    Show that the three points having position vectors
    straight a with rightwards arrow on top space minus space 2 straight b with rightwards arrow on top space space plus space space 3 straight c with rightwards arrow on top comma space space minus 2 space straight a with rightwards arrow on top space plus space 3 space straight b with rightwards arrow on top space plus space 2 space straight c with rightwards arrow on top comma space minus 8 space straight a with rightwards arrow on top space plus space 13 space straight b with rightwards arrow on top are collinear whatever be straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top

    Solution

    Let straight a with rightwards arrow on top space minus space 2 straight b with rightwards arrow on top space plus space 3 space straight c with rightwards arrow on top comma space space space minus 2 space straight a with rightwards arrow on top space plus space 3 space straight b with rightwards arrow on top space plus space 2 space straight c with rightwards arrow on top comma space space minus 8 space straight a with rightwards arrow on top space plus space 13 space straight b with rightwards arrow on top be the position vectors of A, B, C respectively...
    AB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A space equals space minus 2 straight a with rightwards arrow on top space plus space 3 straight b with rightwards arrow on top plus space 2 space straight c with rightwards arrow on top space minus space straight a with rightwards arrow on top space plus space 2 space straight b with rightwards arrow on top space minus space 3 straight c with rightwards arrow on top space equals space minus 3 space straight a with rightwards arrow on top space plus space 5 space straight b with rightwards arrow on top space minus space straight c with rightwards arrow on top
    AC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight A space equals space minus 8 straight a with rightwards arrow on top space plus space 13 space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top space plus space 2 space straight b with rightwards arrow on top space minus space 3 space straight c with rightwards arrow on top space equals space minus 9 straight a with rightwards arrow on top space plus space 15 space straight b with rightwards arrow on top minus 3 space straight c with rightwards arrow on top
    therefore space space space space space AC with rightwards arrow on top space equals space 3 space AB with rightwards arrow on top space space space space space space space rightwards double arrow space space space space AC with rightwards arrow on top space and space AB with rightwards arrow on top space are space parallel space vectors
    But A is their common point
    ∴  point A, B, C are collinear.

    Question 329
    CBSEENMA12034005
    Question 330
    CBSEENMA12034006
    Question 331
    CBSEENMA12034007

    Show that the vectors and straight a with rightwards arrow on top space equals space 3 space straight i with hat on top space minus space 4 space straight j with hat on top space minus space 4 space straight k with hat on top comma space space space space straight b with rightwards arrow on top space equals space 2 straight i with hat on top space minus space straight j with hat on top space plus space straight k with hat on top comma space space straight c with rightwards arrow on top space equals space straight i with hat on top space minus space 3 space straight j with hat on top space minus space 5 space straight k with hat on top form the sides of right angled triangle. 

    Solution
    Let A, B, C be the points whose position vectors are
                  straight a with rightwards arrow on top space equals space 3 space straight i with hat on top space minus space 4 space straight j with hat on top space minus space 4 space straight k with hat on top
straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space straight j with hat on top space plus space straight k with hat on top
straight c with rightwards arrow on top space equals space straight i with hat on top space minus space 3 space straight j with hat on top space minus space 5 space straight k with hat on top space respectively
straight a squared space equals space left parenthesis 3 right parenthesis squared plus left parenthesis negative 4 right parenthesis squared plus left parenthesis negative 4 right parenthesis squared space equals space 9 plus 16 plus 16 space equals space 41
straight b squared space equals space left parenthesis 2 right parenthesis squared plus left parenthesis negative 1 right parenthesis squared plus left parenthesis 1 right parenthesis squared space equals space 4 plus 1 plus 1 space equals space 6
straight c squared space equals space left parenthesis 1 right parenthesis squared plus left parenthesis negative 3 right parenthesis squared plus left parenthesis negative 5 right parenthesis squared space equals space 1 plus 9 plus 25 space equals space 35
    Now,  6 + 35 = 41
    therefore space space space straight b squared space plus space straight c squared equals space space straight a squared
therefore space space space space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top space form space the space sides space of space straight a space right space angled space triangle. space
    Question 332
    CBSEENMA12034008

    Show that the points A, B and C with position vectors, respectively form the vertices of a right angled triangle, stack space straight a with rightwards arrow on top space equals space 3 space straight i with hat on top space minus space 4 space straight j with hat on top space minus space 4 space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space straight j with hat on top space plus space straight k with hat on top space and space straight c with rightwards arrow on top space equals space straight i with hat on top space minus space 3 space straight j with hat on top space space minus space 5 space straight k with hat on top comma space respectively form the vertices of a right angled triangle. 

    Solution
    Let A, B, C, be the points whose position vectors are
                          straight a with rightwards arrow on top space equals space 3 space straight i with hat on top space minus space 4 space straight j with hat on top space minus space 4 space straight k with hat on top
straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space straight j with hat on top space plus space straight k with hat on top
straight c with rightwards arrow on top space equals space straight i with hat on top space minus space 3 space straight j with hat on top space minus space 5 space straight k with hat on top space respectively
         AB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A space equals space straight b with rightwards arrow on top minus straight a with rightwards arrow on top space equals space minus straight i with hat on top plus 3 space straight j with hat on top plus 5 space straight k with hat on top
BC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight B space equals space straight c with rightwards arrow on top space minus space straight b with rightwards arrow on top space equals space minus straight i with hat on top space minus space 2 space straight j with hat on top space minus space 6 space straight k with hat on top
CA with rightwards arrow on top space equals space straight P. straight V. space of space straight A space minus space straight P. straight V. space of space straight C space equals space straight a with rightwards arrow on top space minus space straight c with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space straight j with hat on top space plus space straight k with hat on top
    therefore space space AB with rightwards arrow on top space plus space BC with rightwards arrow on top space plus space CA with rightwards arrow on top space equals space 0 with rightwards arrow on top
therefore space space space space space ABC space is space straight a space triangle.
space space space space space space space space AB space equals space square root of left parenthesis negative 1 right parenthesis squared plus left parenthesis 3 right parenthesis squared plus left parenthesis 5 right parenthesis squared end root space equals space square root of 1 plus 9 plus 25 end root space equals space square root of 35
space space space space space space space space BC space equals space square root of left parenthesis negative 1 right parenthesis squared plus left parenthesis negative 2 right parenthesis squared plus left parenthesis negative 6 right parenthesis squared end root space equals space square root of 1 plus 4 plus 36 end root space equals space square root of 41
space space space space space space space space space CA space equals space square root of left parenthesis 2 right parenthesis squared plus left parenthesis negative 1 right parenthesis squared plus left parenthesis 1 right parenthesis squared end root space equals space square root of 4 plus 1 plus 1 end root space equals space square root of 6
    Now,  CA squared plus AB squared space equals space 6 plus 35 space equals 41 space equals space BC squared
    therefore space space space space increment ABC space is space right space angled space at space straight A.
    Question 333
    CBSEENMA12034009

    Prove that the points straight i with hat on top space minus space straight j with hat on top comma space space 4 straight i with hat on top space minus 3 space straight j with hat on top space plus space straight k with hat on top space and space 2 space straight i with hat on top space minus space 4 space straight j with hat on top space plus space 5 space space straight k with hat on top are the vertices of a right angled triangle. 

    Solution
    Let A, B, C, be the points whose position vectors are
                    straight a with rightwards arrow on top space equals space straight i with hat on top space minus space straight j with hat on top comma space space space straight b with rightwards arrow on top space equals space 4 space straight i with hat on top space minus space 3 space straight j with hat on top space plus space straight k with hat on top comma space space straight c with rightwards arrow on top space equals space 2 space straight i with hat on top space space minus space 4 space straight j with hat on top space plus space 5 space straight k with hat on top
AB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A space equals space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top
space space space space space space space space equals space left parenthesis 4 space straight i with hat on top space minus space 3 space straight j with hat on top space plus space space straight k with hat on top right parenthesis space minus space left parenthesis straight i with hat on top space minus space space straight j with hat on top right parenthesis space equals space 3 space straight i with hat on top space minus space 2 space straight j with hat on top space plus space straight k with hat on top
BC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight B space equals space straight c with rightwards arrow on top space minus space straight b with rightwards arrow on top
space space space space space space space space equals space left parenthesis 2 straight i with hat on top space minus space 4 space straight j with hat on top space plus space 5 space straight k with hat on top right parenthesis space minus space left parenthesis 4 space straight i with hat on top space minus space 3 space straight j with hat on top space plus space straight k with hat on top right parenthesis space equals space minus space 2 straight i with hat on top space minus space straight j with hat on top space plus space 4 space straight k with hat on top
CA with rightwards arrow on top space equals space straight P. straight V. space of space straight A space minus space straight P. straight V. space of space straight C space equals space straight a with rightwards arrow on top space minus space straight c with rightwards arrow on top
space space space space space space space space space space space equals left parenthesis straight i with hat on top space minus space straight j with hat on top right parenthesis space minus space left parenthesis 2 straight i with hat on top space minus space 4 space straight j with hat on top space plus space space 5 space straight k with hat on top right parenthesis space equals space minus straight i with hat on top space plus space 3 space straight j with hat on top space minus space 5 space straight k with hat on top
therefore space space space AB with rightwards arrow on top space plus space BC with rightwards arrow on top space plus space CA with rightwards arrow on top space equals space 0 with rightwards arrow on top
therefore space space space ABC space is space straight a space triangle.
                        AB space equals space square root of 9 plus 4 plus 1 end root space equals space square root of 14
BC space equals space square root of 4 plus 1 plus 16 end root space equals space square root of 21
CA space equals space square root of 1 plus 9 plus 25 end root space equals square root of 35
    Now,  AB squared plus BC squared space equals space CA squared
    therefore space space space increment ABC space is space right space angled space at space straight B.
    Question 334
    CBSEENMA12034010

    Show that the points with position vectors 2 space straight i with hat on top space plus space 6 space straight j with hat on top space plus space 3 space straight k with hat on top comma space space straight i with hat on top space plus space 2 space straight j with hat on top space plus space 7 space straight k with hat on top and 3 straight i with hat on top space plus space 10 space straight j with hat on top space minus space straight k with hat on top are collinear. 

    Solution

    Let straight a with rightwards arrow on top space equals space 2 straight i with hat on top space plus space 6 space straight j with hat on top space plus space space 3 space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space straight i with hat on top space plus space space 2 straight j with hat on top space plus space 7 space straight k with hat on top comma space space space straight c with rightwards arrow on top space equals space 3 straight i with hat on top space plus 10 straight j with hat on top space minus space straight k with hat on top be position vectors of A, B, C respectively.
                      AB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A space equals space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top
                             equals left parenthesis straight i with hat on top space plus 2 space straight j with hat on top space plus space space 7 space straight k with hat on top right parenthesis space minus space left parenthesis 2 space straight i with hat on top space plus space 6 space straight j with hat on top space space plus space 3 space straight k with hat on top right parenthesis space equals space minus space straight i with hat on top space minus space 4 space straight j with hat on top space plus space 4 space straight k with hat on top
                      BC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight B space equals space straight c with rightwards arrow on top space minus space straight b with rightwards arrow on top
space space space space space space equals space left parenthesis 3 space straight i with hat on top space plus space 10 space straight j with hat on top space minus space straight k with hat on top right parenthesis space space minus left parenthesis straight i with hat on top space plus space 2 space straight j with hat on top space space plus space 7 space straight k with hat on top right parenthesis space equals space 2 space straight i with hat on top space plus space space 8 space straight j with hat on top space minus space 8 space straight k with hat on top
    therefore space space space space space BC with rightwards arrow on top space equals space minus space 2 space AB with rightwards arrow on top
    therefore space space space AB with rightwards arrow on top space and space BC with rightwards arrow on top space are space parallel space vectors.
But space straight A space is space their space common space point. space
therefore space space space space space points space straight A comma space straight B comma space straight C space are space collinear.

    Question 335
    CBSEENMA12034011

    Show that the points A (2, 6, 3). B (1, 2, 7) and C (3, 10, – 1) are collinear.

    Solution
    The given points are A (2, 6, 3), B (1, 2, 7) , C (3, 10, –1).
    Let O be origin.
    therefore space space space space OA with rightwards arrow on top space equals space 2 space straight i with hat on top plus space 6 space straight j with hat on top space plus space space 3 space straight k with hat on top comma space space space OB with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top space plus space space 7 space straight k with hat on top
space space space space space space space space OC with rightwards arrow on top space equals space 3 space straight i with hat on top space plus space 10 space straight j with hat on top space minus space straight k with hat on top
space space space space space space space AB with rightwards arrow on top space equals space OB with rightwards arrow on top space minus space OA with rightwards arrow on top space equals space left parenthesis straight i with hat on top space plus space 2 space straight j with hat on top space plus space 7 space straight k with hat on top right parenthesis space minus space left parenthesis 2 space straight j with hat on top space plus space 6 space straight j with hat on top space plus space 3 space straight k with hat on top right parenthesis
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space minus straight i with hat on top space minus space 4 space straight j with hat on top space plus space 4 space straight k with hat on top
space space space space space space space BC with rightwards arrow on top space equals space OC with rightwards arrow on top space minus space OB with rightwards arrow on top space equals space left parenthesis 3 straight i with hat on top space plus space 10 straight j with hat on top space minus space straight k with hat on top right parenthesis space minus space left parenthesis straight i with hat on top space plus space 2 space straight j with hat on top space plus space 7 space straight k with hat on top right parenthesis
space space space space space space space space space space space space space space space equals space 2 straight i with hat on top space plus space 8 space straight j with hat on top space minus space space 8 space straight k with hat on top
therefore space space space space space space BC with rightwards arrow on top space equals space minus 2 space AB with rightwards arrow on top space space space space space space space space space space rightwards double arrow space space space space BC with rightwards arrow on top space equals space 2 space BA with rightwards arrow on top
because space space space space space space BC with rightwards arrow on top space and space BA with rightwards arrow on top space are space parallel space vectors. space
    But B is their common point
    ∴    points A, B, C are collinear.
    Question 336
    CBSEENMA12034012

    The position vectors of the points A, B and C are 2 space straight i with hat on top space plus space straight j with hat on top space minus space straight k with hat on top comma space space space space 3 space straight i with hat on top space minus space 2 space straight j with hat on top space plus space straight k with hat on top comma space space space straight i with hat on top space plus space 4 space straight j with hat on top space minus space 3 space straight k with hat on top respectively. Show that A, B and C are collinear.

    Solution

    Let straight a with rightwards arrow on top space equals space 2 straight i with hat on top space plus space straight j with hat on top space minus space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space 3 space straight i with hat on top space minus space 2 space straight j with hat on top space plus space straight k with hat on top comma space space straight c with rightwards arrow on top space equals space straight i with hat on top space plus space 4 space straight j with hat on top space minus space 3 space straight k with hat on top be position vectors of A, B and C respectively.
         AB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A space equals space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top space equals space open parentheses 3 straight i with hat on top space minus space 2 straight j with hat on top space plus space straight k with hat on top close parentheses space minus space left parenthesis 2 space straight i with hat on top space plus space straight j with hat on top space minus space straight k with hat on top right parenthesis
                                                                                                  equals space straight i with hat on top space minus space 3 space straight j with hat on top space plus space 2 space straight k with hat on top
        AC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight A space equals space straight c with rightwards arrow on top space minus space straight a with rightwards arrow on top space equals space space open parentheses straight i with hat on top space plus space 4 space straight j with hat on top space minus space 3 space straight k with hat on top close parentheses space minus space left parenthesis 2 straight i with hat on top space plus space straight j with hat on top space minus space straight k with hat on top right parenthesis
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals negative space straight i with hat on top space plus space 3 space straight j with hat on top space minus space 2 space straight k with hat on top
therefore space space space space AC with rightwards arrow on top space equals space minus AB with rightwards arrow on top
therefore space space space space AC with rightwards arrow on top space and space AB with rightwards arrow on top space are space parallel space vectors
But space straight A space is space their space common space point.
therefore space space space points space straight A comma space straight B comma space straight C space are space collinear.

    Question 337
    CBSEENMA12034013
    Question 338
    CBSEENMA12034014

    Find the direction cosines of the vector straight i with hat on top space plus space 2 space straight j with hat on top space plus space 3 space straight k with hat on top.

    Solution

     Let      straight a with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top space plus space 3 space straight k with hat on top
     therefore space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space square root of left parenthesis 1 right parenthesis squared plus left parenthesis 2 right parenthesis squared plus left parenthesis 3 right parenthesis squared end root space equals space square root of 1 plus 4 plus 9 end root space equals space square root of 14
therefore space space space space space straight a with hat on top space equals space fraction numerator open vertical bar straight a with rightwards arrow on top close vertical bar over denominator open vertical bar straight a with rightwards arrow on top close vertical bar end fraction space equals space fraction numerator 1 over denominator square root of 14 end fraction left parenthesis straight i with hat on top space plus space 2 space straight j with hat on top space plus space 3 space straight k with hat on top right parenthesis
space space space space space space space space space space space space equals space fraction numerator 1 over denominator square root of 14 end fraction straight i with hat on top space plus space fraction numerator 2 over denominator square root of 14 end fraction straight j with hat on top space plus space fraction numerator 3 over denominator square root of 14 end fraction straight k with hat on top
therefore space space space direction space cosines space of space straight a with rightwards arrow on top space are space fraction numerator 1 over denominator square root of 14 end fraction comma space fraction numerator 2 over denominator square root of 14 end fraction comma space fraction numerator 3 over denominator square root of 14 end fraction.

    Question 339
    CBSEENMA12034015

    Write the direction ratio’s of the vector straight a with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space minus space 2 space straight k with hat on top and hence calculate its direction cosines.

    Solution

           straight a with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space space minus space 2 space straight k with hat on top
    therefore space space space direction space ratios space of space straight a with rightwards arrow on top space are space 1 comma space 1 comma space minus 2.
                         open vertical bar straight a with rightwards arrow on top close vertical bar space equals space square root of left parenthesis 1 right parenthesis squared plus left parenthesis 1 right parenthesis squared plus left parenthesis negative 2 right parenthesis squared end root space equals square root of 1 plus 1 plus 4 end root space equals square root of 6
    therefore space space space space space straight a with hat on top space equals space fraction numerator straight a with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top close vertical bar end fraction space equals space fraction numerator 1 over denominator square root of 6 end fraction left parenthesis straight i with hat on top space plus space straight j with hat on top space minus space 2 space straight k with hat on top right parenthesis space equals space fraction numerator 1 over denominator square root of 6 end fraction straight i with hat on top space plus space fraction numerator 1 over denominator square root of 6 end fraction straight j with hat on top space minus space fraction numerator 2 over denominator square root of 6 end fraction straight k with hat on top
therefore space space space space direction space cosines space of space straight a with rightwards arrow on top space space are space space fraction numerator 1 over denominator square root of 6 end fraction comma space fraction numerator 1 over denominator square root of 6 end fraction comma space space minus fraction numerator 2 over denominator square root of 6 end fraction.

    Question 340
    CBSEENMA12034016

    Show that the direction cosines of a vector equally inclined to the axes OX, OY and OZ are fraction numerator 1 over denominator square root of 3 end fraction comma space fraction numerator 1 over denominator square root of 3 end fraction comma space fraction numerator 1 over denominator square root of 3 end fraction.

    Solution

    Let straight a with rightwards arrow on top space equals space straight a subscript 1 straight i with hat on top space plus space straight a subscript 2 straight j with hat on top space plus space straight a subscript 3 straight k with hat on top be the vector, where straight a subscript 1 comma space straight a subscript 2 comma space straight a subscript 3 are the direction ratios of the vector.
               Since vector is equally inclined to the axes
         therefore space space space space straight a subscript 1 space equals space straight a subscript 2 space equals space straight a subscript 3 space equals space straight p comma space space say.
therefore space space space straight a with rightwards arrow on top space equals space straight p space straight i with hat on top space plus space straight p space straight j with hat on top space plus straight p space straight k with hat on top
therefore space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space square root of straight p squared plus straight p squared plus straight p squared end root space equals space square root of 3 space straight p squared end root space equals space square root of 3 space straight p
therefore space space space space space space space space space space space space space straight a with hat on top space equals space fraction numerator straight a with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top close vertical bar end fraction space equals space fraction numerator straight p over denominator square root of 3 space straight p end fraction straight i with hat on top space plus space fraction numerator straight p over denominator square root of 3 space straight p end fraction straight j with hat on top space plus space fraction numerator straight p over denominator square root of 3 space straight p end fraction straight k with hat on top
space space space space space space space space space space space space space space space space space space space space space equals space fraction numerator 1 over denominator square root of 3 end fraction straight i with hat on top space plus space fraction numerator 1 over denominator square root of 3 end fraction straight j with hat on top space plus space fraction numerator 1 over denominator square root of 3 end fraction straight k with hat on top
    therefore   direction cosines of a vector equally inclined to axes are fraction numerator 1 over denominator square root of 3 end fraction comma space fraction numerator 1 over denominator square root of 3 end fraction comma space fraction numerator 1 over denominator square root of 3 end fraction.

    Question 341
    CBSEENMA12034017

    If straight P with rightwards arrow on top left parenthesis 1 comma space 5 comma space 4 right parenthesis and straight Q with rightwards arrow on top space left parenthesis 4 comma space 1 comma space minus 2 right parenthesis, find the direction ratios of PQ with rightwards arrow on top.

    Solution

    Here,   OP with rightwards arrow on top space equals space straight i with hat on top space plus space 5 space straight j with hat on top space plus space 4 space straight k with hat on top comma space space space OQ with rightwards arrow on top space equals space 4 space straight i with hat on top space plus space straight j with hat on top space minus space 2 space straight k with hat on top
     therefore space space space space space space space space space PQ with rightwards arrow on top space equals space OQ with rightwards arrow on top space minus space OP with rightwards arrow on top space equals space left parenthesis 4 space straight i with hat on top space plus space straight j with hat on top space minus space 2 space straight k with hat on top right parenthesis space minus space left parenthesis straight i with hat on top space plus space 5 space straight j with hat on top space plus space 4 space straight k with hat on top right parenthesis
                                equals space 3 space straight i with hat on top space minus space 4 space straight j with hat on top space minus space 6 space straight k with hat on top
    therefore space space space space direction space ratios space of space PQ with rightwards arrow on top space are space 3 comma space minus 4 comma space minus 6.

    Question 342
    CBSEENMA12034018

    If A (2, – 1, 3), B (8, 5, – 6) and C (4, 1, 0) are the vertices of a triangle. show that
    (i) AB = 3 AC 
    (ii) The direction-cosines of BC with rightwards arrow on top are fraction numerator negative 2 over denominator square root of 17 end fraction comma space fraction numerator negative 2 over denominator square root of 17 end fraction comma space fraction numerator 3 over denominator square root of 17 end fraction.

    Solution
    Let O be the origin.
    A is (2, -1, 3)          rightwards double arrow             OA with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space straight j with hat on top space plus space 3 space straight k with hat on top
    B is (8, 5, -6)          rightwards double arrow             OB with rightwards arrow on top space equals space 8 space straight i with hat on top space plus space 5 space straight j with hat on top space minus space space 6 space straight k with hat on top
    C is (4, 1, 0)            rightwards double arrow              OC with rightwards arrow on top space equals space 4 space straight i with hat on top space plus space straight j with hat on top space plus space 0 space straight k with hat on top space equals space 4 space straight i with hat on top space plus space straight j with hat on top
    (i)  AB with rightwards arrow on top space equals space OB with rightwards arrow on top space minus space OA with rightwards arrow on top space equals space open parentheses 8 space straight i with hat on top space plus space 5 space straight j with hat on top space minus space 6 space straight k with hat on top close parentheses space minus space left parenthesis 2 space straight i with hat on top space minus space straight j with hat on top space plus space space 3 space straight k with hat on top right parenthesis space equals space 6 space straight i with hat on top space plus space 6 space straight j with hat on top space minus 9 space straight k with hat on top
    therefore space space space space space AB space equals space square root of left parenthesis 6 right parenthesis squared plus left parenthesis 6 right parenthesis squared plus left parenthesis negative 9 right parenthesis squared end root space equals space square root of 36 plus 36 plus 81 end root
space space space space space space space space space space space space space space space equals space square root of 153 space equals square root of 9 space cross times space 17 end root space equals space 3 space square root of 17
         AC with rightwards arrow on top space equals space OC with rightwards arrow on top space minus space OA with rightwards arrow on top space equals space left parenthesis 4 space straight i with hat on top space plus space straight j with hat on top right parenthesis space minus space left parenthesis 2 space straight i with hat on top space minus space straight j with hat on top space plus space 3 space straight k with hat on top right parenthesis space equals space 2 space straight i with hat on top space plus space 2 space straight j with hat on top space minus space 3 space straight k with hat on top
    therefore space space space AC space equals space square root of left parenthesis 2 right parenthesis squared plus left parenthesis 2 right parenthesis squared plus left parenthesis negative 3 right parenthesis squared end root space equals space square root of 4 plus 4 plus 9 end root space equals space square root of 17
therefore space space AB space equals space 3 space space AC
    (ii)  BC with rightwards arrow on top space equals space OC with rightwards arrow on top space minus space OB with rightwards arrow on top space equals space left parenthesis 4 space straight i with hat on top space plus space straight j with hat on top right parenthesis space minus space left parenthesis 8 space straight i with hat on top space plus space 5 space straight j with hat on top space minus space 6 space straight k with hat on top right parenthesis space equals space minus 4 space straight i with hat on top space minus space 4 space straight j with hat on top space plus space 6 space straight k with hat on top
    therefore space space space BC space equals space square root of left parenthesis negative 4 right parenthesis squared plus left parenthesis negative 4 right parenthesis squared plus left parenthesis 6 right parenthesis squared end root space equals square root of 16 plus 16 plus 36 end root space equals square root of 68 equals space square root of 4 space cross times 17 end root space equals space 2 space square root of 17
therefore space space space space space straight a space unit space vector space along space BC with rightwards arrow on top space equals space fraction numerator BC with rightwards arrow on top over denominator open vertical bar BC with rightwards arrow on top close vertical bar end fraction space equals fraction numerator BC with rightwards arrow on top over denominator BC end fraction
                                     equals space fraction numerator 1 over denominator 2 square root of 17 end fraction left parenthesis negative 4 space straight i with hat on top space minus space 4 space straight j with hat on top space plus space 6 space straight k with hat on top right parenthesis space equals space minus fraction numerator 2 over denominator square root of 17 end fraction straight i with hat on top space minus space fraction numerator 2 over denominator square root of 17 end fraction straight j with hat on top space plus space fraction numerator 3 over denominator square root of 17 end fraction straight k with hat on top
    therefore space space space direction cosines of BC with rightwards arrow on top i.e.,   coeffs. of straight i with hat on top comma space straight j with hat on top comma space straight k with hat on top  are negative fraction numerator 2 over denominator square root of 17 end fraction comma space minus fraction numerator 2 over denominator square root of 17 end fraction comma space fraction numerator 3 over denominator square root of 17 end fraction.

    Question 343
    CBSEENMA12034019

    Show that vector straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top is equally inclined to the axes OX. OY and OZ. 

    Solution

    Let straight a with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space plus space space straight k with hat on top
     therefore space space space space space straight a with rightwards arrow on top space equals space square root of left parenthesis 1 right parenthesis squared plus left parenthesis 1 right parenthesis squared plus left parenthesis 1 right parenthesis squared end root space equals space square root of 1 plus 1 plus 1 end root space equals square root of 3
therefore space space space space straight a with hat on top space equals space fraction numerator straight a over denominator open vertical bar straight a with rightwards arrow on top close vertical bar end fraction space equals space fraction numerator 1 over denominator square root of 3 end fraction left parenthesis straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top right parenthesis space equals space fraction numerator 1 over denominator square root of 3 end fraction straight i with hat on top space plus space fraction numerator 1 over denominator square root of 3 end fraction straight j with hat on top space plus space fraction numerator 1 over denominator square root of 3 end fraction straight k with hat on top
therefore space space space space direction space cosines space of space straight a with rightwards arrow on top space are space fraction numerator 1 over denominator square root of 3 end fraction comma space fraction numerator 1 over denominator square root of 3 end fraction comma space fraction numerator 1 over denominator square root of 3 end fraction
therefore space space space space cos space straight alpha space equals fraction numerator 1 over denominator square root of 3 end fraction comma space space cos space straight beta space equals space fraction numerator 1 over denominator square root of 3 end fraction comma space space cos space straight gamma space equals space fraction numerator 1 over denominator square root of 3 end fraction
    where straight alpha comma space straight beta comma space straight gamma are angles made by vector with axes.
    therefore space space space space cos space straight alpha space equals space cos space straight beta space equals space cos space straight gamma
rightwards double arrow space space space space space space space space space straight alpha space equals straight beta space equals straight gamma
therefore space space space space given space vector space is space equally space inclined space to space the space axes space OX comma space OY comma space OZ.

    Question 344
    CBSEENMA12034020

    Show that the points A (6. – 7, 0) B (16, – 19, – 4). C (0, 3, – 6), D (2, – 5, 10) are such that AB and CD intersect at the point P (1, – 1, 2).

    Solution
    We are given the points A (6, – 7, 0), B (16, – 19, – 4), C (0, 3, – 6),  D (2, – 5. 10), P (1, – 1, 2).
     AB with rightwards arrow on top space equals space PV space of space straight B space minus space straight P. straight V. space of space straight A space equals space left parenthesis 16 space straight i with hat on top space minus space 19 space straight j with hat on top space minus space 4 space straight k with hat on top right parenthesis space minus space left parenthesis 6 space straight i with hat on top space minus space 7 space straight j with hat on top space plus space 0 space straight k with hat on top right parenthesis
space space space space space space space equals space 10 space straight i with hat on top space minus space 12 space straight j with hat on top space minus space 4 space straight k with hat on top
AP with rightwards arrow on top space equals space straight P. straight V. space of space straight P space minus space straight P. straight V. space of space straight A space equals space left parenthesis straight i with hat on top space minus space straight j with hat on top space minus space space 2 space straight k with hat on top right parenthesis space minus space left parenthesis 6 space straight i with hat on top space minus space 7 space straight j with hat on top space plus space 0 space straight k with hat on top right parenthesis
space space space space space space space equals space minus space 5 space straight i with hat on top space plus space 6 space straight j with hat on top space space plus space 2 space straight k with hat on top
PB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight P space equals space left parenthesis 16 space straight i with hat on top space minus space 19 space straight j with hat on top space minus space 4 space straight k with hat on top right parenthesis space minus space left parenthesis straight i with hat on top space minus space straight j with hat on top space plus space 2 space straight k with hat on top right parenthesis
space space space space space space space equals space 5 space straight i with hat on top space minus space 18 space straight j with hat on top space minus space 6 space straight k with hat on top
therefore space space AB space equals space open vertical bar AB with rightwards arrow on top close vertical bar space equals space square root of 100 plus 144 plus 16 end root space equals space square root of 260 space equals space square root of 4 space cross times space 65 end root space equals space 2 square root of 65
space space space space space space AP space equals space open vertical bar AP with rightwards arrow on top close vertical bar space equals space square root of 25 plus 36 plus 4 end root space equals square root of 65
space space space space space space PB space equals space open vertical bar PB with rightwards arrow on top close vertical bar space equals space square root of 225 plus 324 plus 36 end root space equals space square root of 585 space equals square root of 9 space cross times space 65 end root space equals 3 square root of 65
    therefore space space space space BA plus space AP space equals space BP
therefore space space space space straight P comma space straight A comma space straight B space are space collinear.
    Again CD with rightwards arrow on top space equals space straight P. straight V. space of space straight D space minus space straight P. straight V. space of space straight C space equals space left parenthesis 2 straight i with hat on top space minus space 5 space straight j with hat on top space plus space 10 space straight k with hat on top right parenthesis space minus space left parenthesis 3 space straight j with hat on top space minus space 6 space straight k with hat on top right parenthesis
                       equals space 2 space straight i with hat on top space minus space 8 space straight j with hat on top space plus space 16 space straight k with hat on top
                CP with rightwards arrow on top space equals space straight P. straight V. space of space straight P space minus space straight P. straight V. space of space straight C space equals space left parenthesis straight i with hat on top space minus space straight j with hat on top space plus space 2 space straight k with hat on top right parenthesis space minus space left parenthesis 3 space straight j with hat on top space minus space 6 space straight k with hat on top right parenthesis
space space space space space space space equals space straight i with hat on top space minus space 4 space straight j with hat on top space plus space 8 space straight k with hat on top
               PD with rightwards arrow on top space equals space straight P. straight V. space of space straight D space minus space straight P. straight V. space of space straight P space equals space open parentheses 2 space straight i with hat on top space minus space 5 space straight j with hat on top space plus space 10 space straight k with hat on top close parentheses space minus space left parenthesis straight i with hat on top space minus space straight j with hat on top space plus space 2 space straight k with hat on top right parenthesis
space space space space space space equals space straight i with hat on top space minus space 4 space straight j with hat on top space plus space 8 space straight k with hat on top
    therefore space space space space CD space equals open vertical bar CD with rightwards arrow on top close vertical bar space equals space square root of 4 plus 64 plus 256 end root space equals square root of 324 space equals 18
space space space space space space space space CP space equals space open vertical bar CP with rightwards arrow on top close vertical bar space equals space square root of 1 plus 16 plus 64 end root space equals space square root of 81 equals space 9
space space space space space space space space space PD equals space open vertical bar PD with rightwards arrow on top close vertical bar space equals space square root of 1 plus 16 plus 64 end root space equals square root of 81 space equals 9
therefore space space space space CP plus PD space equals space CD space space space space rightwards double arrow space space space space straight P comma space straight C comma space straight D space are space collinear.
therefore space space space space AB space and space CD space intersect space at space straight P left parenthesis 1 comma space minus 1 comma space space 2 right parenthesis.

    Question 345
    CBSEENMA12034021

    The vectors of magnitude a, 2a, 3a meet at a point and their directions arc. along the diagonals of three adjacent faces of a cube. Determine the magnitude of their resultant.

    Solution

    Let straight i with hat on top comma space straight j with hat on top comma space straight k with hat on top be unit vectors along OA, OC, OE respectively. Let OB, OD, OF be the diagonals of faces OABC, OCDE, OEFA respectively of the cube of side of length b.

      Now  OB with rightwards arrow on top space equals OA with rightwards arrow on top space plus space AB with rightwards arrow on top space equals space OA with rightwards arrow on top space plus space OC with rightwards arrow on top space equals space straight b space straight i with hat on top space plus space straight b space straight j with hat on top
    therefore space space space open vertical bar OB with rightwards arrow on top close vertical bar space equals space square root of straight b squared plus straight b squared end root space equals space square root of 2 space straight b squared end root space equals space square root of 2 space straight b
         therefore   unit vector along
                      OB with rightwards arrow on top space equals space fraction numerator OB with rightwards arrow on top over denominator open vertical bar OB with rightwards arrow on top close vertical bar end fraction equals space fraction numerator straight b space straight i with hat on top space plus space straight b space straight j with hat on top over denominator square root of 2 space straight b end fraction space equals space fraction numerator 1 over denominator square root of 2 end fraction left parenthesis straight i with hat on top space plus space straight j with hat on top right parenthesis
          Similarly unit vector along OD with rightwards arrow on top = fraction numerator 1 over denominator square root of 2 end fraction left parenthesis straight j with hat on top plus straight k with hat on top right parenthesis
      and unit vector along OF with rightwards arrow on top space equals space fraction numerator 1 over denominator square root of 2 end fraction left parenthesis straight k with hat on top space plus space straight i with hat on top right parenthesis
           therefore space space space space space OB with rightwards arrow on top space equals space fraction numerator straight a with rightwards arrow on top over denominator square root of 2 end fraction left parenthesis straight i with hat on top space plus space straight j with hat on top right parenthesis comma space space space space OD with rightwards arrow on top space equals space fraction numerator 2 straight a over denominator square root of 2 end fraction left parenthesis straight j with hat on top space plus straight k with hat on top right parenthesis comma space space OF with rightwards arrow on top space equals space fraction numerator 3 straight a over denominator square root of 2 end fraction left parenthesis straight k with hat on top space plus space straight i with hat on top right parenthesis
    Let straight R with rightwards arrow on top be resultant of vectors OB with rightwards arrow on top comma space OD with rightwards arrow on top comma space OF with rightwards arrow on top
    therefore space space space space space space space straight R with rightwards arrow on top space equals space OB with rightwards arrow on top space plus space OD with rightwards arrow on top space plus space OF with rightwards arrow on top
space space space space space space space space space space space space space space space space equals fraction numerator straight a over denominator square root of 2 end fraction left parenthesis straight i with hat on top space plus space straight j with hat on top right parenthesis space fraction numerator 2 straight a over denominator square root of 2 end fraction left parenthesis straight j with hat on top space plus space straight k with hat on top right parenthesis space plus space fraction numerator 3 straight a over denominator square root of 2 end fraction left parenthesis straight k with hat on top space plus space straight i with hat on top right parenthesis
space space space space space space space space space space space space space space space space equals space fraction numerator 4 straight a over denominator square root of 2 end fraction straight i with hat on top space plus space fraction numerator 3 straight a over denominator square root of 2 end fraction straight j with hat on top space plus space fraction numerator 5 straight a over denominator square root of 2 end fraction straight k with hat on top
    therefore      magnitude of resultant vector =  open vertical bar straight R with rightwards arrow on top close vertical bar
                                  equals space square root of open parentheses fraction numerator 4 straight a over denominator square root of 2 end fraction close parentheses squared plus open parentheses fraction numerator 3 space straight a over denominator square root of 2 end fraction close parentheses squared plus space open parentheses fraction numerator 5 straight a over denominator square root of 2 end fraction close parentheses squared end root
equals space square root of fraction numerator 16 straight a squared over denominator 2 end fraction plus fraction numerator 9 straight a squared over denominator 2 end fraction plus fraction numerator 25 space straight a squared over denominator 2 end fraction end root space equals space square root of 25 space straight a squared end root space equals space 5 space straight a
                          
                         
     

    Question 346
    CBSEENMA12034022

    Write all the unit vectors in XY-plane.

    Solution

    Let straight r with rightwards arrow on top space equals space straight x space straight i with hat on top space plus space space straight y space straight j with hat on top space be a unit vector OP with rightwards arrow on top in XY - plane.
                      therefore space space space space space space OP space equals open vertical bar straight r with rightwards arrow on top close vertical bar space equals space 1
straight P space is space left parenthesis straight x comma space straight y right parenthesis
    From P draw PM space perpendicular space OX.
    In rt. angled increment OMP comma
                    straight x over 1 space equals space cos space straight theta comma space space space straight y over 1 space equals space sin space straight theta

    therefore space straight x space equals space cos space straight theta comma space space space straight y space equals space sin space straight theta
therefore space space straight r with rightwards arrow on top space equals space left parenthesis cos space straight theta right parenthesis space straight i with hat on top space plus space left parenthesis sin space straight theta right parenthesis space straight j with hat on top space space space... left parenthesis 1 right parenthesis
Here space open vertical bar straight r with rightwards arrow on top close vertical bar space equals space square root of cos squared straight theta plus space sin squared straight theta end root space equals square root of 1 space equals space 1
    Also, as straight theta varies from 0 to straight pi, the point P traces the circle r2 + y2 = 1 counterclockwise, and this covers all possible directions.
    ∴    (1) gives every unit vector in the XY-plane.

    Question 347
    CBSEENMA12034023

    Write down a unit vector in XY-plane, making an angle of 30° with the positive direction of x-axis.

    Solution

    Let straight r with rightwards arrow on top space equals space straight x space straight i with hat on top space plus space straight y space straight j with hat on top be a unit vector OP
    therefore space space space space OP space equals space open vertical bar straight r with rightwards arrow on top close vertical bar space equals space space 1
    straight P space is left parenthesis straight x comma space straight y right parenthesis.
    From P draw PM space perpendicular space OX.
    In rt. angled increment OMP comma

                 straight x over 1 space equals space cos space 30 degree space space space or space space space straight x space equals space fraction numerator square root of 3 over denominator 2 end fraction
    and     straight y over 1 space equals space sin space 30 degree space space space space or space space space straight y space equals space 1 half
    therefore space space space space straight r with rightwards arrow on top space equals space fraction numerator square root of 3 over denominator 2 end fraction straight i with hat on top space space plus space 1 half straight j with hat on top.

    Question 348
    CBSEENMA12034024

    A girl walks 4 km towards west, then she walks 3 km in a direction 30° east of north and stops. Determine the girl’s displacement from her initial point of departure.

    Solution
    Let | OA | = 4 km and | AB | = 3 km then ∠OAB = 90° – 30° = 60°.

    From B,  draw BM perpendicular OA.
    Let  straight x space straight i with hat on top space plus space straight y space straight j with hat on top be the position vector of B.
    therefore space space space space space space space space space space space space space space space space space space space space open vertical bar straight x close vertical bar space equals space open vertical bar OM close vertical bar space equals space open vertical bar OA close vertical bar space minus space open vertical bar MA close vertical bar
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space 4 space minus space left parenthesis open vertical bar straight A space straight B close vertical bar space cos space 60 degree right parenthesis
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space 4 minus 3 space open parentheses 1 half close parentheses space equals space 5 over 2 space
therefore space space space space space space space space space space space space space space straight x space equals space minus 5 over 2
    Also               straight y space equals space MB space equals space open vertical bar straight A thin space straight B close vertical bar space sin space 60 degree space equals space fraction numerator 3 space square root of 3 over denominator 2 end fraction.
    therefore             OB with rightwards arrow on top space equals space straight x straight i with hat on top space plus space straight y space straight j with hat on top space equals space minus 5 over 2 straight i with hat on top space plus fraction numerator 3 square root of 3 over denominator 2 end fraction straight j with hat on top
    Distance of B from initial point equals space open vertical bar OB close vertical bar space equals space open vertical bar OB with rightwards arrow on top close vertical bar
                                   equals space open vertical bar negative 5 over 2 straight i with hat on top space plus space fraction numerator 3 square root of 3 over denominator 2 end fraction straight j with hat on top close vertical bar space equals space square root of open parentheses fraction numerator negative 5 over denominator 2 end fraction close parentheses squared plus space open parentheses fraction numerator 3 space square root of 3 over denominator 2 end fraction close parentheses squared end root

equals space square root of 25 over 4 plus 27 over 4 end root space equals square root of fraction numerator 25 plus 27 over denominator 4 end fraction end root
equals space square root of 52 over 4 end root space equals square root of 13 space km.
    Question 349
    CBSEENMA12034025

    If straight a with rightwards arrow on top space equals straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top,  then is true that open vertical bar straight a with rightwards arrow on top close vertical bar space equals space open vertical bar straight b with rightwards arrow on top close vertical bar space plus space open vertical bar straight c with rightwards arrow on top close vertical bar space ? Justify your answer.

    Solution

    When straight a with rightwards arrow on top space equals space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top, then straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top form a triangle ABC where
                            AB with rightwards arrow on top space equals space straight b with rightwards arrow on top comma space space BC with rightwards arrow on top space equals space straight c with rightwards arrow on top comma space space AC with rightwards arrow on top space equals space straight a with rightwards arrow on top
     
    Since sum of two sides of a triangle is always greater than the third side
                  therefore space space space space open vertical bar straight b with rightwards arrow on top close vertical bar space plus space open vertical bar straight c with rightwards arrow on top close vertical bar space greater than space open vertical bar straight a with rightwards arrow on top close vertical bar
or space space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space less than space open vertical bar straight b with rightwards arrow on top close vertical bar space plus space open vertical bar straight c with rightwards arrow on top close vertical bar
therefore space space space straight a with rightwards arrow on top space equals straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top space does space not space imply space in space general space that space open vertical bar straight a with rightwards arrow on top close vertical bar space equals open vertical bar straight b with rightwards arrow on top close vertical bar space plus space open vertical bar straight c with rightwards arrow on top close vertical bar.

    Question 350
    CBSEENMA12034026

    In triangle ABC, which of the following is not true

    • AB with rightwards arrow on top space plus space BC with rightwards arrow on top space plus space CA with rightwards arrow on top space equals space 0 with rightwards arrow on top
    • AB with rightwards arrow on top space plus space BC with rightwards arrow on top space minus space AC with rightwards arrow on top space equals space 0 with rightwards arrow on top
    • AB with rightwards arrow on top space plus space BC with rightwards arrow on top space minus space CA with rightwards arrow on top space equals space 0 with rightwards arrow on top
    • AB with rightwards arrow on top space minus space CB with rightwards arrow on top space plus space CA with rightwards arrow on top space equals space 0 with rightwards arrow on top

    Solution

    C.

    AB with rightwards arrow on top space plus space BC with rightwards arrow on top space minus space CA with rightwards arrow on top space equals space 0 with rightwards arrow on top In ∆ABC, by triangle law of forces, we have
                         AB with rightwards arrow on top space plus space BC with rightwards arrow on top space plus space CA with rightwards arrow on top space equals space 0 with rightwards arrow on top
    or                 AB with rightwards arrow on top space plus space BC with rightwards arrow on top space minus space AC with rightwards arrow on top space equals space 0
    or                 AB with rightwards arrow on top space minus space CB with rightwards arrow on top space plus space CA with rightwards arrow on top space equals space 0 with rightwards arrow on top
    therefore space space space left parenthesis straight C right parenthesis space is space not space true.
    Question 352
    CBSEENMA12034028

    If straight a with rightwards arrow on top is a non-zero vector of magnitude ‘a’ and λ a non-zero scalar, then straight lambda straight a with rightwards arrow on top is a unit vector if

    • straight lambda space equals space 1
    • straight lambda equals negative 1
    • straight a space equals space open vertical bar straight lambda close vertical bar
    • straight a space equals fraction numerator 1 over denominator open vertical bar straight lambda close vertical bar end fraction

    Solution

    D.

    straight a space equals fraction numerator 1 over denominator open vertical bar straight lambda close vertical bar end fraction

    Since straight a with rightwards arrow on top is a non-zero vector of magnitude a
      therefore space space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space straight a
    Now,   straight lambda space straight a with rightwards arrow on top is a unit vector if open vertical bar straight lambda straight a with rightwards arrow on top close vertical bar space equals space 1
    i.e.   if  open vertical bar straight lambda close vertical bar space open vertical bar straight a with rightwards arrow on top close vertical bar space equals 1
    i.e.  if  open vertical bar straight lambda close vertical bar space straight a space equals space 1
    i.e. if    straight a space equals space fraction numerator 1 over denominator open vertical bar straight lambda close vertical bar end fraction space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space left parenthesis straight lambda space not equal to space 0 right parenthesis
    therefore space space space left parenthesis straight D right parenthesis space is space correct space answer.

    Question 353
    CBSEENMA12034029

    Find the position vector of a point R which divides the line joining straight P left parenthesis 3 straight a with rightwards arrow on top space minus space 2 space straight b with rightwards arrow on top right parenthesis space and space straight Q left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis in the ratio 2 : 1 
    (i) internally and (ii) externally.

    Solution
    Given points are straight P left parenthesis 3 straight a with rightwards arrow on top space minus space 2 straight b with rightwards arrow on top right parenthesis comma space space straight Q left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis
    (i) The position vector of the point R dividing the join of P and Q internally in the 
      ratio  2 : 1 is

      
    (ii) The  position vector of the point R dividing the join of P and Q externally in the ratio 2 : 1 is



    Question 354
    CBSEENMA12034030

    Find the position vector of a point R which divides the line joining two points straight P left parenthesis 2 straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis space and space straight Q left parenthesis straight a with rightwards arrow on top space minus space 3 space straight b with rightwards arrow on top right parenthesis externally in the ratio 1 :2. Also, show that P is the middle point of the line segment RQ.

    Solution
    The position vector of R which divides the join of P open parentheses 2 straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close parentheses space and space straight Q left parenthesis straight a with rightwards arrow on top space minus space 3 space straight b with rightwards arrow on top right parenthesis externally in the ratio 1 : 2 i.e. internally in the ratio 1 : 2 is 
    fraction numerator 1 left parenthesis straight a with rightwards arrow on top space minus space 3 space straight b with rightwards arrow on top right parenthesis minus space 2 left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis over denominator 1 minus 2 end fraction space space space space straight i. straight e. space space space 3 straight a with rightwards arrow on top space plus space 5 straight b with rightwards arrow on top
    Mid-point of RQ is
    fraction numerator left parenthesis 3 straight a with rightwards arrow on top space plus space 5 space straight b with rightwards arrow on top right parenthesis space plus space left parenthesis straight a with rightwards arrow on top space minus space 3 space straight b with rightwards arrow on top right parenthesis over denominator 2 end fraction space space space space space straight i. straight e. space space space 20 space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top
    which is position vector of P.
    Hence the result.
    Question 355
    CBSEENMA12034031

    Find the position vector of a point R which divides the line joining two points P and Q whose position vectors are straight i with hat on top space plus space 2 space straight j with hat on top space minus space straight k with hat on top and negative straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top respectively, in the ratio 2 : 1
    (i) internally                  (ii) externally

    Solution

    Let straight a with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top space minus space straight k with hat on top and straight b with rightwards arrow on top space equals space minus straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top be position vectors of P and Q respectively.
    (i) The position vector of the point R dividing the join of P and Q internally in the ratio 2 : 1 is
                     fraction numerator 2 straight b with rightwards arrow on top space plus space 1 left parenthesis straight a with rightwards arrow on top right parenthesis over denominator 2 plus 1 end fraction space straight i. straight e. space space fraction numerator 2 left parenthesis negative straight i with hat on top plus space straight j with hat on top space plus space straight k with hat on top right parenthesis space plus space 1 left parenthesis straight i with hat on top space plus space 2 space straight j with hat on top space minus space straight k with hat on top right parenthesis over denominator 3 end fraction
    i.e..      1 third left parenthesis negative straight i with hat on top space plus space space 4 space straight j with hat on top space plus space straight k with hat on top right parenthesis space space straight i. straight e. comma space space minus 1 third straight i with hat on top space plus space 4 over 3 straight j with hat on top space plus space 1 third straight k with hat on top
    (ii) The position vector of the point R dividing the join of P and Q externally in the ratio 2 : 1 i.e.. internally in the ratio 2 : – 1 is 

    fraction numerator 2 left parenthesis straight b with rightwards arrow on top right parenthesis space minus space 1 left parenthesis straight a with rightwards arrow on top right parenthesis over denominator 2 plus left parenthesis negative 1 right parenthesis end fraction space straight i. straight e. space space space fraction numerator 2 left parenthesis negative straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top right parenthesis space minus space 1 left parenthesis straight i with hat on top space plus space 2 space straight j with hat on top space minus space straight k with hat on top right parenthesis over denominator 2 minus 1 end fraction
straight i. straight e. space fraction numerator negative 3 space straight i with hat on top space plus space 3 space straight k with hat on top over denominator 1 end fraction space space space straight i. straight e. space space space minus 3 space straight i with hat on top space plus space 3 space straight k with hat on top

    Question 356
    CBSEENMA12034032

    If straight a with rightwards arrow on top an straight b with rightwards arrow on top are position vectors of points A and B respectively, then find the position vector of points of trisection of AB.

    Solution
    Let P and Q be the points of trisection of AB. Then P divides AB in the ration 1 : 2 and Q divides AB in the ratio 2 : 1.

         P.V. of P = fraction numerator left parenthesis 1 right parenthesis space left parenthesis straight b with rightwards arrow on top right parenthesis space plus space left parenthesis 2 right parenthesis thin space left parenthesis straight a with rightwards arrow on top right parenthesis over denominator 1 plus 2 end fraction space equals space fraction numerator 2 straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top over denominator 3 end fraction
          P.V. of Q = fraction numerator left parenthesis 2 right parenthesis space left parenthesis straight b with rightwards arrow on top right parenthesis space plus space left parenthesis 1 right parenthesis thin space left parenthesis straight a with rightwards arrow on top right parenthesis over denominator 2 plus 1 end fraction space equals fraction numerator straight a with rightwards arrow on top space plus space 2 space straight b with rightwards arrow on top over denominator 3 end fraction
    Question 357
    CBSEENMA12034033

    Find the position vector of the mid-point of the vector joining the points P (2, 3, 4) and Q(4, 1, – 2).

    Solution

    Let straight a with rightwards arrow on top space and space straight b with rightwards arrow on top be position vectors of points P(2, 3, 4) and Q(4, 1, -2) respectively.
                         therefore space space space space straight a with rightwards arrow on top space equals space 2 straight i with hat on top space plus space 3 space straight j with hat on top space plus space 4 space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space 4 space straight i with hat on top space plus space straight j with hat on top space minus space 2 space straight k with hat on top
    Position vector of mid-point of PQ is
             fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top over denominator 2 end fraction space straight i. straight e. comma space fraction numerator left parenthesis 2 space straight i with hat on top space plus space 3 space straight j with hat on top space plus space 4 space straight k with hat on top right parenthesis space plus space left parenthesis 4 space straight i with hat on top space plus space straight j with hat on top space minus space 2 space straight k with hat on top right parenthesis over denominator 2 end fraction
    i.e. fraction numerator 6 space straight i with hat on top space plus space 4 space straight j with hat on top space plus space 2 space straight k with hat on top over denominator 2 end fraction    i.e.,  3 space straight i with hat on top space plus space 2 space straight j with hat on top space plus space straight k with hat on top

    Question 358
    CBSEENMA12034034

    Find the vector from the origin O to the centroid of the triangle whose vertices are (1, – 1, 2), (2, 1, 3) and (–1, 2, –1).

    Solution

    Let straight a with rightwards arrow on top space equals space straight i with hat on top space minus space straight j with hat on top space plus space 2 space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space straight j with hat on top space plus space 3 space straight k with hat on top comma space space straight c with rightwards arrow on top space equals space minus straight i with hat on top space plus space 2 space straight j with hat on top space minus space straight k with hat on top be the position vectors of vertices A, B, C respectively. 
    Position vector straight d with rightwards arrow on top of centroid is given by
     straight d with rightwards arrow on top space equals space fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 3 end fraction
space space space space space space equals space fraction numerator left parenthesis straight i with hat on top space minus space straight j with hat on top space plus space 2 space straight k with hat on top right parenthesis space plus space left parenthesis 2 space straight i with hat on top space space plus space straight j with hat on top space plus 3 space straight k with hat on top right parenthesis space plus space left parenthesis negative straight i with hat on top space plus space 2 space straight j with hat on top space minus space straight k with hat on top right parenthesis over denominator 3 end fraction space equals space fraction numerator 2 stack straight i space with hat on top plus 2 space straight j with hat on top space plus space 4 space straight k with hat on top over denominator space 3 end fraction

    Question 359
    CBSEENMA12034035

    Show that the three points A (1, –2, –8) , B (5. 0. –2) and C (11, 3. 7) are collinear and find the ratio in which B divides AC.

    Solution

    Given points are A (1, –2, –8), B (5, 0, –2), C (11, 3, 7).
    Let O be origin.
                     OA with rightwards arrow on top space equals space straight i with hat on top space minus space 2 space straight j with hat on top space minus space 8 space straight k with hat on top comma space space OB with rightwards arrow on top space equals space 5 space straight i with hat on top space minus space 2 space straight k with hat on top comma space space OC with rightwards arrow on top space equals space 11 space straight i with hat on top space plus space 3 space straight j with hat on top space plus space 7 space straight k with hat on top
AB with rightwards arrow on top space equals space OB with rightwards arrow on top space minus space OA with rightwards arrow on top space equals space left parenthesis 5 space straight i with hat on top space minus space 2 space straight k with hat on top right parenthesis space minus space left parenthesis straight i with hat on top space minus space 2 space straight j with hat on top space minus space 8 space straight k with hat on top right parenthesis space equals space 4 space straight i with hat on top space plus space 2 space straight j with hat on top space plus space 6 space straight k with hat on top
AC with rightwards arrow on top space equals space OC with rightwards arrow on top space minus space OA with rightwards arrow on top space equals space left parenthesis 11 space straight i with hat on top space plus space 3 space straight j with hat on top space plus space 7 space straight k with hat on top right parenthesis space minus space left parenthesis straight i with hat on top space minus space 2 space straight j with hat on top space minus space 8 space straight k with hat on top right parenthesis
space space space space space space space equals space 10 space straight i with hat on top space plus space 5 space straight j with hat on top space plus space 15 space straight k with hat on top
    therefore space space space AC with rightwards arrow on top space equals space 5 over 2 left parenthesis 4 space straight i with hat on top space plus space 2 space straight j with hat on top space plus space 6 space straight k with hat on top right parenthesis space equals space 5 over 2 AB with rightwards arrow on top
therefore space space space AC with rightwards arrow on top space and space AB with rightwards arrow on top space are space parallel space vectors

     But A is their common point.
    ∴    points A. B. C are collinear and B divides AC in the ratio 2 : 3.
    Question 360
    CBSEENMA12034036

    If Q is the point of intersection of the medians of the triangle ABC, then prove that QA with rightwards arrow on top space plus space QB with rightwards arrow on top space plus space QC with rightwards arrow on top space equals space 0 with rightwards arrow on top.

    Solution

    Let straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top be the position vectors of vertices A, B, C respectively. Then position vector of centroid Q is fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 3 end fraction.
    L.H.S.  = QA with rightwards arrow on top space plus space OB with rightwards arrow on top space plus space QC with rightwards arrow on top
               equals space left parenthesis straight P. straight V. space of space straight A space minus space straight P. straight V. space of space straight Q right parenthesis space plus space left parenthesis straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight Q right parenthesis space plus space left parenthesis straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight Q right parenthesis
        equals space open parentheses straight a with rightwards arrow on top space minus space fraction numerator straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 3 end fraction close parentheses space plus space open parentheses straight b with rightwards arrow on top space minus space fraction numerator straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top over denominator 3 end fraction close parentheses space plus space open parentheses straight c with rightwards arrow on top space minus space fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 3 end fraction close parentheses
equals space open parentheses straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top close parentheses space minus space 3 space open parentheses fraction numerator straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top over denominator 3 end fraction close parentheses
space equals space left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top right parenthesis space minus space left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top right parenthesis space equals space 0 with rightwards arrow on top space equals space straight R. straight H. straight S.

    Question 361
    CBSEENMA12034037

    ABCD is a parallelogram. E, F are mid-points of BC, CD respectively. AE, AF meet the diaginal BD at Q, P respectively. Show that PQ trisects DB.

    Solution
    Take A as origin. Let straight b with rightwards arrow on top comma space straight c with rightwards arrow on top comma space straight d with rightwards arrow on top be the position vectors of B, C, D respectively. Let M be the point of intersection of diagonals of AC and BD.
    In ∆ADC, P is the centroid as it is the point of intersection of two medians AF and DM as M is midpoint of AC.

    therefore space space space AP with rightwards arrow on top space equals space fraction numerator 0 with rightwards arrow on top space plus space straight d with rightwards arrow on top space plus space straight c with rightwards arrow on top over denominator 3 end fraction space equals space fraction numerator 2 space straight d with rightwards arrow on top space plus straight b with rightwards arrow on top over denominator 3 end fraction
    ∴   P divides BD in the ratio 2 : 1
    Similarly Q divides DB in the ratio 2 : 1
    Hence the result.
    Question 362
    CBSEENMA12034038

    If straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space stack straight c comma with rightwards arrow on top straight d with rightwards arrow on top are any four vectors in 3 - dimensional space with the same initial point and such that 3 space straight a with rightwards arrow on top space space minus space 2 space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top space minus space 2 space straight d with rightwards arrow on top space equals space 0 with rightwards arrow on top comma space show that terminals, A, B, C, D of these vectors are coplanar. Find the point at which AC and BD meet. Find the ratio in which P divides AC and BD.

    Solution

    Since,   3 space straight a with rightwards arrow on top space minus space 2 space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top space minus space 2 space straight d with rightwards arrow on top space equals space 0 with rightwards arrow on top
    therefore space space space space 3 space straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top space equals space 2 space straight b with rightwards arrow on top space plus space 2 space straight d with rightwards arrow on top
     rightwards double arrow space space space fraction numerator 3 space straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top over denominator 4 end fraction space equals space fraction numerator 2 space straight b with rightwards arrow on top space plus space 2 space straight d with rightwards arrow on top over denominator 4 end fraction space space space rightwards double arrow space space space space space fraction numerator 3 space straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top over denominator 3 plus 1 end fraction space equals space fraction numerator straight b with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction
    ∴    P.V. of point dividing AC in the ratio 1 : 3 is the same as the P.V. of mid-point of BD.
    ∴    AC and BD intersect at P whose P.V. is fraction numerator 3 straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top over denominator 4 end fraction space or space space fraction numerator straight b with rightwards arrow on top space plus space straight d with rightwards arrow on top over denominator 2 end fraction. This point P divides AC in the ratio 3:1 and BD in the ratio 1:1.

    Question 363
    CBSEENMA12034039

    Four points A, B, C, D with position vectors straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top comma space straight d with rightwards arrow on top respectively are such that 3 straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space plus space space 2 straight c with rightwards arrow on top space minus space 4 space straight d with rightwards arrow on top space equals space 0 with rightwards arrow on top. Show that the four points are coplanar. Also, find the position vector of the point of intersection of lines AC and BD.

    Solution

    Since,       3 space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space plus space 2 space straight c with rightwards arrow on top space minus space 4 space straight d with rightwards arrow on top space equals space 0 with rightwards arrow on top
    therefore space space 3 space straight a with rightwards arrow on top space plus space 2 space straight c with rightwards arrow on top space equals space straight b with rightwards arrow on top space plus space 4 space straight d with rightwards arrow on top space space space rightwards double arrow space space fraction numerator 3 space straight a with rightwards arrow on top space plus space 2 space straight c with rightwards arrow on top over denominator 5 end fraction space equals fraction numerator straight b with rightwards arrow on top space plus space 4 space straight d with rightwards arrow on top over denominator 5 end fraction space rightwards double arrow space space fraction numerator 3 space straight a with rightwards arrow on top space plus space 2 space straight c with rightwards arrow on top over denominator 3 plus 2 end fraction space equals space fraction numerator straight b with rightwards arrow on top space plus 4 space straight d with rightwards arrow on top over denominator 1 plus 4 end fraction

    ⇒ P.V. of point dividing AC in the ratio 2 : 3 is the same as the P.V. of point dividing BD in the ratio 4 : 1
    ∴  AC and BD intersect at P i.e., A, B, C, D are coplanar and P has P.V. as
    fraction numerator 3 straight a with rightwards arrow on top space plus space 2 straight c with rightwards arrow on top over denominator 5 end fraction space space or space space fraction numerator straight b with rightwards arrow on top space plus space 4 space straight d with rightwards arrow on top over denominator 5 end fraction

    Question 364
    CBSEENMA12034040

    The mid-points of two opposite sides of a quadrilateral and the mid-points of the diagonals are the vertices of a parallelogram. Prove using vectors.

    Solution

    Let straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top comma space straight d with rightwards arrow on top be position vectors of vertices A, B, C, D repsectively.
    Let E, F, G, H be mid-points of AB, CD, AC, BD respectively.
    P.V. of E = fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top over denominator 2 end fraction
    P.V. of F = fraction numerator straight c with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction
    P.V. of G = fraction numerator straight a with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction
    P.V. of H = fraction numerator straight b with rightwards arrow on top space plus straight d with rightwards arrow on top over denominator 2 end fraction

    EG with rightwards arrow on top space equals space straight P. straight V. of space straight G space minus space straight P. straight V. space of space straight E space equals space fraction numerator straight a with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction minus fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top over denominator 2 end fraction space equals fraction numerator straight c with rightwards arrow on top minus straight b with rightwards arrow on top over denominator 2 end fraction
HF with rightwards arrow on top space equals space straight P. straight V. space of space straight F space minus space straight P. straight V. space of space straight H space equals space fraction numerator straight c with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction minus fraction numerator straight b with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction space equals fraction numerator straight c with rightwards arrow on top minus straight b with rightwards arrow on top over denominator 2 end fraction
    therefore space space space space EG with rightwards arrow on top space equals space HF with rightwards arrow on top space space space space space rightwards double arrow space space space space EG thin space vertical line vertical line thin space HF space and space EG space equals space HF space space space space rightwards double arrow space space space EGHF space is space straight a space parallelogram. space

    Question 365
    CBSEENMA12034041

    A point P divides a line segment AB in the ratio A : 1. Give the values of A for which
    P lies in between AB and 
    (i) nearer A than B    (ii) nearer B than A

    Solution
    Since P lies in between AB and P is nearer A than B.
    therefore space space space space AP space less than thin space BP space space space straight i. straight e. space AP over BP less than 1
therefore space space space straight lambda space less than space 1. space space space Also space straight lambda space greater than 0
therefore space space space 0 space less than space straight lambda space less than space 1.
    If P is nearer to B than A, then AP greater than BP space space straight i. straight e. space space AP over BP greater than 1 space comma space space straight i. straight e. space space space space straight lambda space greater than space 1.
    Question 366
    CBSEENMA12034042

    A point P divides a line segment AB in the ratio A : 1. Give the values of A for which P lies outside AB and 
    (i) nearer A than B    (ii) nearer B than A.

    Solution

    When P lies outside AB and is nearer to A than B. then AP<PB.
    Also division is external
    ∴   – 1 < λ < 0
    When P is nearer to B than A, the AP > PB
    ∴  λ < – I

    Question 367
    CBSEENMA12034043

    Show that the lines joining the mid-points of the opposite sides of a quadrilateral bisect each other.

    Solution

    Let straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top comma space straight d with rightwards arrow on top be position vectors of vertices A, B, C, D of quadrilateral ABCD.
                  Let P, Q, R, S be mid-points of the sides AB, BC, CD, DA respectively of quadrilateral ABCD.
             therefore space space space space position vectors of P, Q, R, S are

                     fraction numerator straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top over denominator 2 end fraction comma space fraction numerator straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction comma space fraction numerator straight c with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction comma space fraction numerator straight d with rightwards arrow on top plus straight a with rightwards arrow on top over denominator 2 end fraction respectively.
              Position vectors of mid - point of PR is
                                  fraction numerator begin display style fraction numerator straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top over denominator 2 end fraction end style plus begin display style fraction numerator straight c with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction end style over denominator 2 end fraction space straight i. straight e. space space fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 4 end fraction
            Position vector of mid- point of QS is
                                   fraction numerator begin display style fraction numerator straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction end style plus begin display style fraction numerator straight d with rightwards arrow on top plus straight a with rightwards arrow on top over denominator 2 end fraction end style over denominator 2 end fraction space space space space straight i. straight e. space space fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 4 end fraction
    Since position vector of mid-points of PR and QS is same.
    ∴    lines joining the mid-points of the opposite sides of a quadrilateral bisect each other.

    Question 368
    CBSEENMA12034044

    Show that a quadrilateral is a parallelogram if an only if diagonals bisect each other.

    Solution
    (i) Assume that quadrilateral ABCD is a parallelogram.
     Let straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top comma space straight d with rightwards arrow on top be the position vectors of A, B, C and D respectively with reference to O as the origin.
    because space space ABCD space is space straight a space parallelogram
therefore space space space AB space equals space DC space and space AB thin space vertical line vertical line thin space DC
therefore space space space AB with rightwards arrow on top space equals space DC with rightwards arrow on top
therefore space space space space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A
space space space space space space space space space space space space space space space space space space space space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight D
therefore space space space space space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top space equals space straight c with rightwards arrow on top space minus straight d with rightwards arrow on top
therefore space space space straight b with rightwards arrow on top plus straight d with rightwards arrow on top space equals space straight a with rightwards arrow on top plus straight c with rightwards arrow on top
therefore space space space space equals space fraction numerator straight b with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction space equals fraction numerator straight a with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction

    ∴ P.V. of mid-point of diagonal BD = P.V. of mid-point of diagonal AC.
    ∴ diagonal AC and BD bisect each other.
    (ii) Assume that the diagonals AC and BD of the quadrilateral bisect each other.
    ∴   P.V. of mid-point of diagonal BD = P.V. of mid-point of diagonal AC.
    therefore space space fraction numerator straight b with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction space equals space fraction numerator straight a with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction
therefore space space space space straight b with rightwards arrow on top space plus space straight d with rightwards arrow on top space equals space straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top
therefore space space space space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top space equals space straight c with rightwards arrow on top space minus space straight d with rightwards arrow on top
therefore space space space space OB with rightwards arrow on top space minus space OA with rightwards arrow on top space equals space OC with rightwards arrow on top space minus space OD with rightwards arrow on top
therefore space space space space space AB with rightwards arrow on top space equals space DC with rightwards arrow on top
therefore space space space AB space equals space DC space and space AB thin space vertical line vertical line thin space DC
therefore space space space ABCD space is space straight a space parallelogram

    Question 369
    CBSEENMA12034045

    Prove, using vectors, that the line segment joining the mid-points of the non-parallel sides of a trapezium is parallel to the bases and is equal to half the sum of their lenghts.

    Solution

    Let straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top comma space straight d with rightwards arrow on top be the position vectors of the vertices A, B, C, D of the trapezium in which AB||CD
    Now AB || CD
      rightwards double arrow space space AB with rightwards arrow on top space equals space straight lambda space DC with rightwards arrow on top
    where straight lambda is some scalar.
      therefore space space space space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A space equals space space straight lambda space left parenthesis straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight D right parenthesis
rightwards double arrow space space space space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top space equals straight lambda left parenthesis straight c with rightwards arrow on top space minus space straight d with rightwards arrow on top right parenthesis space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis

    Let E be mid-point of AD and F be mid-point of BC.
    therefore space space space straight P. straight V. space of space straight E space equals space fraction numerator straight a with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction space and space straight P. straight V. space of space straight F space equals fraction numerator straight b with rightwards arrow on top space plus straight c with rightwards arrow on top over denominator 2 end fraction
    therefore space space space space space EF with rightwards arrow on top space equals space straight P. straight V. space of space straight F space minus space straight P. straight V. space of space straight E space equals space fraction numerator straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top over denominator 2 end fraction space minus space fraction numerator straight a with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction
space space space space space space space space space space space space space space equals space fraction numerator straight b with rightwards arrow on top plus straight c with rightwards arrow on top minus straight a with rightwards arrow on top minus straight d with rightwards arrow on top over denominator 2 end fraction space equals fraction numerator open parentheses straight b with rightwards arrow on top minus straight a with rightwards arrow on top close parentheses space plus left parenthesis straight c with rightwards arrow on top minus straight d with rightwards arrow on top right parenthesis over denominator 2 end fraction space equals fraction numerator straight lambda space left parenthesis straight c with rightwards arrow on top minus straight d with rightwards arrow on top right parenthesis space plus space left parenthesis straight c with rightwards arrow on top minus straight d with rightwards arrow on top right parenthesis over denominator 2 end fraction
space space space space space space space space space space space space space space equals space open parentheses fraction numerator straight lambda plus 1 over denominator 2 end fraction close parentheses space space left parenthesis straight c with rightwards arrow on top space minus space straight d with rightwards arrow on top right parenthesis space equals space fraction numerator straight lambda plus 1 over denominator 2 end fraction DC with rightwards arrow on top
    ∴     EF and DC are parallel.
    Also EF is parallel to AB as AB is parallel to DC.
    Now, EF space equals space fraction numerator straight lambda plus 1 over denominator 2 end fraction DC space equals fraction numerator straight lambda. space DC space plus DC over denominator 2 end fraction space rightwards double arrow space space space EF space equals space fraction numerator AB plus DC over denominator 2 end fraction
    Hence the result. 

    Question 370
    CBSEENMA12034046

    The mid-points of two opposite sides of a quadrilateral and the mid-points of the diagonals are the vertices of a parallelogram. Prove using vectors.

    Solution

    Let straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top comma space straight d with rightwards arrow on top be position vectors of vertices A, B, C, D respectively.
    Let E, F, G, H be mid-points of AB, CD, AC, BD respectively.
    P.V. of E = fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top over denominator 2 end fraction
    P.V. of F = fraction numerator straight c with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction
    straight P. straight V. space of space straight G space equals space fraction numerator straight a with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction
straight P. straight V. space of space straight H space equals space fraction numerator straight b with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction


    EG with rightwards arrow on top space equals space straight P. straight V. space of space straight G space minus space straight P. straight V. space of space straight E space equals space fraction numerator straight a with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction space minus fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top over denominator 2 end fraction space equals space fraction numerator straight c with rightwards arrow on top minus straight b with rightwards arrow on top over denominator 2 end fraction
HF with rightwards arrow on top space equals space straight P. straight V. space of space straight F space minus space straight P. straight V. space of thin space straight H space equals space fraction numerator straight c with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction space minus space fraction numerator straight b with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction space equals space fraction numerator straight c with rightwards arrow on top minus straight b with rightwards arrow on top over denominator 2 end fraction
therefore space space space space space EG with rightwards arrow on top space equals space HF with rightwards arrow on top space space space rightwards double arrow space space space space EG thin space vertical line vertical line thin space HF space and space EG space equals space HF space space space space rightwards double arrow space space EGHF space is space straight a space parallelogram

    Question 371
    CBSEENMA12034047

    If D, E and F are the mid-points of the sides of a triangle ABC, show that OA with rightwards arrow on top space plus space OB with rightwards arrow on top space plus space OC with rightwards arrow on top space equals space OD with rightwards arrow on top space plus space OE with rightwards arrow on top space plus space OF with rightwards arrow on top, where O is any arbitrary point.

    Solution
    Take O as origin.
    Let straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top be position vectors of vertices A, B, C respectively.
                        therefore space space space space space space OA with rightwards arrow on top space equals space straight a with rightwards arrow on top comma
space space space space space space space space space space OB with rightwards arrow on top space equals space straight b with rightwards arrow on top comma space OC with rightwards arrow on top space equals space straight c with rightwards arrow on top

    Position vectors of D, E, F are
                                   fraction numerator straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction comma space fraction numerator straight c with rightwards arrow on top plus straight a with rightwards arrow on top over denominator 2 end fraction comma space fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top over denominator 2 end fraction space respectively.
    therefore space space space space OD with rightwards arrow on top space equals space fraction numerator straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction comma space OE with rightwards arrow on top space equals fraction numerator straight c with rightwards arrow on top plus straight a with rightwards arrow on top over denominator 2 end fraction comma space OF with rightwards arrow on top space equals fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top over denominator 2 end fraction
space space space straight L. straight H. straight S. space equals space OA with rightwards arrow on top plus OB with rightwards arrow on top plus OC with rightwards arrow on top space equals space straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top
space space space straight R. straight H. straight S. space equals space OD with rightwards arrow on top plus OE with rightwards arrow on top plus OF with rightwards arrow on top
space space space space space space space space space space space space space space space space space equals space fraction numerator straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction plus fraction numerator straight c with rightwards arrow on top plus straight a with rightwards arrow on top over denominator 2 end fraction plus fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top over denominator 2 end fraction space equals fraction numerator straight b with rightwards arrow on top plus straight c with rightwards arrow on top plus straight c with rightwards arrow on top plus straight a with rightwards arrow on top plus straight a with rightwards arrow on top plus straight b with rightwards arrow on top over denominator 2 end fraction
space space space space space space space space space space space space space space space space space space space equals space fraction numerator 2 left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis over denominator 2 end fraction space equals space straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top
straight L. straight H. straight S. space equals space straight R. straight H. straight S.
    Question 372
    CBSEENMA12034048

    The points D, E, F divide the sides BC, CA. AB of a triangle in the ratio 1 : 4, 3 : 2 and 3 : 7 respectively. Show that the sum of the vectors AB with rightwards arrow on top comma space BE with rightwards arrow on top space and space CF with rightwards arrow on top is parallel to CK with rightwards arrow on top comma space where K divides AB in the ratio 1 : 3.

    Solution

    Let straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top be position vectors of A, B, C respectively.
             P.V. of D = fraction numerator 1. space straight c with rightwards arrow on top space plus space 4. space straight b with rightwards arrow on top over denominator 1 plus 4 end fraction space equals space fraction numerator straight c with rightwards arrow on top plus 4 space straight b with rightwards arrow on top over denominator 5 end fraction
             straight P. straight V. space of space straight E space equals space fraction numerator 3 space straight a with rightwards arrow on top space plus space 2 space straight c with rightwards arrow on top over denominator 3 plus 2 end fraction space equals fraction numerator 3 space straight a with rightwards arrow on top space plus space 2 space straight c with rightwards arrow on top over denominator 5 end fraction
straight P. straight V. space of space straight F space equals space fraction numerator 3 space straight b with rightwards arrow on top space plus space 7 space straight a with rightwards arrow on top over denominator 3 plus 7 end fraction space equals fraction numerator 3 space straight b with rightwards arrow on top space plus space space 7 space straight a with rightwards arrow on top over denominator 10 end fraction
straight P. straight V. space of space straight K space equals space fraction numerator 1. space straight b with rightwards arrow on top space plus space 3. space straight a with rightwards arrow on top over denominator 1 plus 3 end fraction space equals fraction numerator straight b with rightwards arrow on top space plus space 3 space straight a with rightwards arrow on top over denominator 4 end fraction
    AB with rightwards arrow on top space plus space BE with rightwards arrow on top space plus space CF with rightwards arrow on top space equals space left parenthesis straight P. straight V. space of space straight D space minus space straight P. straight V. of space straight A right parenthesis space plus space left parenthesis straight P. straight V. space of space straight E space minus space straight P. straight V. space of space straight B right parenthesis
                                                                                     + (P.V. of F - P.V. of C)

                 equals space open parentheses fraction numerator straight c with rightwards arrow on top plus 4 space straight b with rightwards arrow on top over denominator 5 end fraction minus straight a with rightwards arrow on top close parentheses space plus space open parentheses fraction numerator 3 space straight a with rightwards arrow on top space plus space 2 space straight c with rightwards arrow on top over denominator 5 end fraction minus straight b with rightwards arrow on top close parentheses space plus space open parentheses fraction numerator 3 space straight b with rightwards arrow on top space plus space space 7 space straight a with rightwards arrow on top over denominator 10 end fraction space minus straight c with rightwards arrow on top close parentheses
equals space fraction numerator 2 space straight c with rightwards arrow on top plus 8 space straight b with rightwards arrow on top minus 10 space straight a with rightwards arrow on top space plus space 6 straight a with rightwards arrow on top plus 4 straight c with rightwards arrow on top minus 10 straight b with rightwards arrow on top plus 3 straight b with rightwards arrow on top plus 7 straight a with rightwards arrow on top minus 10 straight c with rightwards arrow on top space over denominator 10 end fraction equals space fraction numerator 3 straight a with rightwards arrow on top plus straight b with rightwards arrow on top minus 4 straight c with rightwards arrow on top over denominator 10 end fraction
    CK with rightwards arrow on top space equals space straight P. straight V. space of space straight K space minus space straight P. straight V. space of space straight C
             equals space fraction numerator straight b with rightwards arrow on top space plus space 3 space straight a with rightwards arrow on top over denominator 4 end fraction space minus space straight c with rightwards arrow on top space equals space fraction numerator straight b plus 3 straight a with rightwards arrow on top space minus space 4 straight c with rightwards arrow on top over denominator 4 end fraction space equals fraction numerator 3 straight a with rightwards arrow on top plus straight b with rightwards arrow on top minus 4 straight c with rightwards arrow on top over denominator 4 end fraction
equals space 5 over 2 cross times fraction numerator 3 straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top minus 4 straight c with rightwards arrow on top over denominator 10 end fraction space equals 5 over 2 open parentheses AD with rightwards arrow on top space plus space BE with rightwards arrow on top space plus space CF with rightwards arrow on top close parentheses
AD with rightwards arrow on top plus BE with rightwards arrow on top space plus space CF with rightwards arrow on top space is space parallel space to space CK with rightwards arrow on top.

    Question 373
    CBSEENMA12034049

    Show that the line joining one vertex of a parallelogram to the mid-point of an opposite side trisects the diagonal and is trisected there at.

    Solution
    Let OABC be a parallelogram Table O as origin. Let straight a with rightwards arrow on top and straight b with rightwards arrow on top be position vectors of straight A with rightwards arrow on top space and space straight C with rightwards arrow on top such that OA with rightwards arrow on top space equals space straight a with rightwards arrow on top comma space OC with rightwards arrow on top space equals space straight b with rightwards arrow on top.
         Now,  OB with rightwards arrow on top space equals space OA with rightwards arrow on top space plus space AB with rightwards arrow on top space equals space OA with rightwards arrow on top space plus space OC with rightwards arrow on top
                  therefore space space space space OB with rightwards arrow on top space equals straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top
therefore space space space space space position space vector space of space straight B space is space open parentheses straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close parentheses.
    Position vector of mid-point of D of A is fraction numerator straight a with rightwards arrow on top over denominator 2 end fraction

    P.V. of a point dividing CD in the ratio
                     2 : 1 is fraction numerator 2 space open parentheses begin display style fraction numerator straight a with rightwards arrow on top over denominator 2 end fraction end style close parentheses space plus space left parenthesis 1 right parenthesis thin space left parenthesis straight b with rightwards arrow on top right parenthesis over denominator 2 plus 1 end fraction space space straight i. straight e. space space fraction numerator straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top over denominator 3 end fraction
    Again position vector of point divides OB in the ratio 1: 2 is
                              fraction numerator left parenthesis 1 right parenthesis thin space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space plus space 2 left parenthesis stack 0 right parenthesis with rightwards arrow on top over denominator 1 plus 2 end fraction space straight i. straight e. space fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top over denominator 3 end fraction
    ∴  position vectors of points trisecting CD and OB are same.
    ∴  CD trisects OB and CD is trisected there at.
    Question 374
    CBSEENMA12034050

    If P and Q are the mid-points of the sides AB and CD of a parallelogram ABCD, prove that DP and BQ cut the diagonal AC in its points of trisection which are also the points of trisection of DP and BQ respectively.

    Solution
    Take A as origin. Let straight b with rightwards arrow on top space and space straight d with rightwards arrow on top be position vectors of B and D respectively such that
    AB with rightwards arrow on top space equals space straight b with rightwards arrow on top comma space space AD with rightwards arrow on top space equals space straight d with rightwards arrow on top

    Now position vector of P, mid-point of AB, is fraction numerator straight d with rightwards arrow on top over denominator 2 end fraction.
    Also,    AQ with rightwards arrow on top space equals space AD with rightwards arrow on top space plus space DQ with rightwards arrow on top space equals space AD with rightwards arrow on top space space plus space 1 half DC with rightwards arrow on top space equals AD with rightwards arrow on top space plus space 1 half AB with rightwards arrow on top space equals space straight d with rightwards arrow on top space plus space 1 half straight b with rightwards arrow on top
    therefore  position vector of Q is straight d with rightwards arrow on top space plus space fraction numerator straight b with rightwards arrow on top over denominator 2 end fraction
                  AC with rightwards arrow on top space equals space AB with rightwards arrow on top space plus space BC with rightwards arrow on top space equals space AB with rightwards arrow on top space plus space AD with rightwards arrow on top space equals space straight b with rightwards arrow on top plus straight d with rightwards arrow on top
    Let E divide AC in the ratio 1 : 2 and F divide AC in the ratio 2 : 1
    therefore position vector of E is fraction numerator 1 left parenthesis straight b with rightwards arrow on top plus straight d with rightwards arrow on top right parenthesis space plus space 2 left parenthesis stack 0 right parenthesis with rightwards arrow on top over denominator 1 plus 2 end fraction space equals space fraction numerator straight b with rightwards arrow on top space plus space straight d with rightwards arrow on top over denominator 3 end fraction
    Position vector of point dividing PD in the ratio 1:2 is fraction numerator left parenthesis 1 right parenthesis space straight d with rightwards arrow on top space plus left parenthesis 2 right parenthesis open parentheses begin display style fraction numerator straight b with rightwards arrow on top over denominator 2 end fraction end style close parentheses over denominator 1 plus 2 end fraction space equals fraction numerator straight b with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 3 end fraction
    Position vector of straight F with rightwards arrow on top is fraction numerator 2 left parenthesis straight b with rightwards arrow on top plus straight d with rightwards arrow on top right parenthesis space plus space 1 left parenthesis 0 with rightwards arrow on top right parenthesis over denominator 1 plus 2 end fraction space equals space fraction numerator 2 straight b with rightwards arrow on top plus 2 straight d with rightwards arrow on top over denominator 3 end fraction
    Position vector of point dividing BQ in the ratio 2 : 1 is fraction numerator 2 space open parentheses straight d with rightwards arrow on top plus begin display style fraction numerator straight b with rightwards arrow on top over denominator 2 end fraction end style close parentheses plus space 1 left parenthesis straight b with rightwards arrow on top right parenthesis over denominator 2 plus 1 end fraction equals space fraction numerator 2 straight b with rightwards arrow on top space plus space 2 straight d with rightwards arrow on top over denominator 3 end fraction
     ∴    DP and BQ cut diagonal AC in its points of trisection which are also the points of trisection of DP and BQ respectively.
    Question 375
    CBSEENMA12034051

    Points E and F are taken on the sides BC and CD of a parallelogram ABCD such that open vertical bar BF with rightwards arrow on top close vertical bar thin space colon thin space open vertical bar FC with rightwards arrow on top close vertical bar space equals space straight mu comma space space space space open vertical bar DE with rightwards arrow on top close vertical bar space colon thin space open vertical bar EC with rightwards arrow on top close vertical bar space equals space straight lambdaThe straight lines FD and AE intersect at the point O. Find the ratio open vertical bar FO with rightwards arrow on top close vertical bar space colon thin space open vertical bar OD with rightwards arrow on top close vertical bar.

    Solution
    Take A as origin. Let straight b with rightwards arrow on top and straight d with rightwards arrow on top be position vectors of B and D respectively.
    Now,     AC with rightwards arrow on top space equals space AB with rightwards arrow on top space plus space BC with rightwards arrow on top
     therefore space space AC with rightwards arrow on top space equals space AB with rightwards arrow on top space plus space AD with rightwards arrow on top
therefore space space space AC with rightwards arrow on top space equals space straight b with rightwards arrow on top plus straight d with rightwards arrow on top
therefore space space space space straight P. straight V. space of space straight C space is space left parenthesis straight b with rightwards arrow on top plus straight d with rightwards arrow on top right parenthesis
straight F space divides space BC space in space the space ratio space straight mu space colon space 1.
therefore space space space space space straight F space is space open parentheses fraction numerator straight mu space left parenthesis straight b with rightwards arrow on top plus straight d with rightwards arrow on top right parenthesis space plus space 1. space straight b with rightwards arrow on top over denominator straight mu plus 1 end fraction close parentheses
space space space space space space space space space straight i. straight e. space open parentheses fraction numerator left parenthesis straight mu plus 1 right parenthesis space straight b with rightwards arrow on top space plus space straight mu space straight d with rightwards arrow on top over denominator straight mu plus 1 end fraction close parentheses
Again space straight E space divides space DC space in space the space ratio space straight lambda space colon 1 space.
therefore space straight E space is space open parentheses fraction numerator straight lambda left parenthesis straight b with rightwards arrow on top plus straight d with rightwards arrow on top right parenthesis space plus space 1. space straight d with rightwards arrow on top over denominator straight lambda plus 1 end fraction close parentheses space space straight i. straight e. space space open parentheses fraction numerator straight lambda straight b with rightwards arrow on top space plus space left parenthesis straight lambda plus 1 right parenthesis space straight d with rightwards arrow on top over denominator straight lambda plus 1 end fraction close parentheses
Now space FD space and space AE space intersect space at space straight O.
Let space DO space colon space OF space space equals space straight k subscript 1 colon 1 space space space and space AO thin space colon thin space OE space equals space straight k subscript 2 colon 1
    therefore space space space fraction numerator straight k subscript 1 open parentheses begin display style fraction numerator left parenthesis straight mu plus 1 right parenthesis space straight b with rightwards arrow on top space plus space straight mu space straight d with rightwards arrow on top over denominator straight mu plus 1 end fraction end style close parentheses plus 1. space straight d with rightwards arrow on top over denominator straight k subscript 1 plus 1 end fraction space equals space fraction numerator straight k subscript 2 open parentheses begin display style fraction numerator left parenthesis straight lambda plus 1 right parenthesis space straight d with rightwards arrow on top plus space straight lambda space straight b with rightwards arrow on top over denominator straight lambda plus 1 end fraction end style close parentheses plus 1. space 0 with rightwards arrow on top over denominator straight k subscript 2 plus 1 end fraction
therefore space space space fraction numerator straight k subscript 1 left parenthesis straight mu plus 1 right parenthesis space straight b with rightwards arrow on top space plus space left parenthesis straight k subscript 1 straight mu space plus space straight mu plus 1 right parenthesis space straight d with rightwards arrow on top over denominator left parenthesis straight k subscript 1 plus 1 right parenthesis thin space left parenthesis straight mu plus 1 right parenthesis end fraction space equals fraction numerator straight k subscript 2 left parenthesis straight lambda plus 1 right parenthesis space straight d with rightwards arrow on top space plus space straight k subscript 2 space straight lambda space straight b with rightwards arrow on top over denominator left parenthesis straight k subscript 2 plus 1 right parenthesis thin space left parenthesis straight lambda plus 1 right parenthesis end fraction
therefore space space space fraction numerator straight k subscript 1 left parenthesis straight mu plus 1 right parenthesis over denominator left parenthesis straight k subscript 1 plus 1 right parenthesis thin space left parenthesis straight mu plus 1 right parenthesis end fraction straight b with rightwards arrow on top space plus space fraction numerator left parenthesis straight k subscript 1 space straight mu space plus space straight mu space plus 1 right parenthesis over denominator left parenthesis straight k subscript 1 plus 1 right parenthesis thin space left parenthesis straight mu plus 1 right parenthesis end fraction straight d with rightwards arrow on top space equals fraction numerator straight k subscript 2 straight lambda over denominator left parenthesis straight k subscript 2 plus 1 right parenthesis thin space left parenthesis straight lambda plus 1 right parenthesis end fraction straight d with rightwards arrow on top space plus space fraction numerator straight k subscript 2 left parenthesis straight lambda plus 1 right parenthesis over denominator left parenthesis straight k subscript 2 plus 1 right parenthesis thin space left parenthesis straight lambda plus 1 right parenthesis end fraction straight b with rightwards arrow on top
rightwards double arrow space space space space space space space space space space space space space space space space space space space fraction numerator straight k subscript 1 left parenthesis straight mu plus 1 right parenthesis over denominator left parenthesis straight k subscript 1 plus 1 right parenthesis thin space left parenthesis straight mu plus 1 right parenthesis end fraction space equals fraction numerator straight k subscript 2 straight lambda over denominator left parenthesis straight k subscript 2 plus 1 right parenthesis space left parenthesis straight lambda plus 1 right parenthesis end fraction
or space space space space space space space space space space space space space space space space space fraction numerator straight k subscript 1 over denominator straight k subscript 1 plus 1 end fraction space equals space fraction numerator straight k subscript 2 straight lambda over denominator left parenthesis straight k subscript 2 plus 1 right parenthesis thin space left parenthesis straight lambda plus 1 right parenthesis end fraction space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
and space space space fraction numerator straight k subscript 1 straight mu plus straight mu plus 1 over denominator left parenthesis straight k subscript 1 plus 1 right parenthesis thin space left parenthesis straight mu plus 1 right parenthesis end fraction space equals fraction numerator straight k subscript 2 over denominator straight k subscript 2 plus 1 end fraction space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis

    rightwards double arrow space space space space space space space space space space space space space space space straight k subscript 1 space equals space fraction numerator straight k subscript 1 straight mu space plus space straight mu space plus 1 over denominator straight mu plus 1 end fraction. space fraction numerator straight lambda over denominator straight lambda plus 1 end fraction
rightwards double arrow space space space space space space space space space space space space space space space space straight k subscript 1 space equals space fraction numerator straight k subscript 1 space straight lambda space straight mu over denominator left parenthesis straight lambda plus 1 right parenthesis thin space left parenthesis straight mu plus 1 right parenthesis end fraction plus fraction numerator straight lambda left parenthesis straight mu plus 1 right parenthesis over denominator left parenthesis straight lambda plus 1 right parenthesis thin space left parenthesis straight mu plus 1 right parenthesis end fraction
rightwards double arrow space space space space space straight k subscript 1 open square brackets 1 minus fraction numerator straight lambda space straight mu over denominator left parenthesis straight lambda plus 1 right parenthesis thin space left parenthesis straight mu plus 1 right parenthesis end fraction close square brackets space equals space fraction numerator straight lambda space left parenthesis straight mu plus 1 right parenthesis over denominator left parenthesis straight lambda plus 1 right parenthesis thin space left parenthesis straight mu plus 1 right parenthesis end fraction
rightwards double arrow space space space straight k subscript 1 open square brackets fraction numerator left parenthesis straight lambda plus 1 right parenthesis thin space left parenthesis straight mu plus 1 right parenthesis space minus space λμ over denominator left parenthesis straight lambda plus 1 right parenthesis thin space left parenthesis straight mu plus 1 right parenthesis end fraction close square brackets space equals space fraction numerator straight lambda left parenthesis straight mu plus 1 right parenthesis over denominator left parenthesis straight lambda plus 1 right parenthesis thin space left parenthesis straight mu plus 1 right parenthesis end fraction
rightwards double arrow space space space straight k subscript 1 fraction numerator straight lambda plus straight mu plus 1 over denominator left parenthesis straight lambda plus 1 right parenthesis thin space left parenthesis straight mu plus 1 right parenthesis end fraction space equals space fraction numerator straight lambda left parenthesis straight mu plus 1 right parenthesis over denominator left parenthesis straight lambda plus 1 right parenthesis thin space left parenthesis straight mu plus 1 right parenthesis end fraction
rightwards double arrow space space space straight k subscript 1 left parenthesis straight lambda plus straight mu plus 1 right parenthesis space equals space straight lambda left parenthesis straight mu plus 1 right parenthesis space space space space space space space space rightwards double arrow space space space space space straight k subscript 1 space equals space fraction numerator straight lambda space left parenthesis straight mu plus 1 right parenthesis over denominator straight lambda plus straight mu plus 1 end fraction
therefore space space space space space open vertical bar FO with rightwards arrow on top close vertical bar space colon space open vertical bar OD with rightwards arrow on top close vertical bar space equals space fraction numerator straight lambda plus straight mu plus 1 over denominator straight lambda left parenthesis straight mu plus 1 right parenthesis end fraction
    Question 376
    CBSEENMA12034052

    Prove that the vertices straight a with rightwards arrow on top space equals space 3 space straight i with hat on top space plus space straight j with hat on top space minus space 2 space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space minus space straight i with hat on top space plus space 3 space straight j with hat on top space plus space 4 space straight k with hat on top and straight c with rightwards arrow on top space equals space 4 space straight i with hat on top space minus space 2 space straight j with hat on top space minus space 6 space straight k with hat on top can form the sides of a triangle. Find the lengths of the medians of the triangle.

    Solution
    Let A, B, C be the points whose position vectors are
                                    straight a with rightwards arrow on top space equals space 3 space straight i with hat on top space plus space straight j with hat on top space minus space 2 space straight k with hat on top comma space straight b with rightwards arrow on top space equals space minus straight i with hat on top space plus space 3 space straight j with hat on top space plus space 4 space straight k with hat on top comma space space space straight c with rightwards arrow on top space equals space 4 space straight i with hat on top space minus space 2 space straight j with hat on top space minus space 6 space straight k with hat on top
       AB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A space equals space straight b with rightwards arrow on top minus straight a with rightwards arrow on top space equals space minus 4 space straight i with hat on top space plus 2 space straight j with hat on top space minus space 6 space straight k with hat on top
BC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight B space equals space straight c with rightwards arrow on top minus straight b with rightwards arrow on top space equals space 5 space straight i with hat on top space minus 5 space straight j with hat on top space minus space 10 space straight k with hat on top
CA with rightwards arrow on top space equals space straight P. straight V. space of space straight A space minus space straight P. straight V. space of space straight C space equals space straight a with rightwards arrow on top space minus space straight c with rightwards arrow on top space equals space minus straight i with hat on top space plus space 3 space straight j with hat on top space plus space 4 space straight k with hat on top
    therefore space space space AB with rightwards arrow on top space plus space BC with rightwards arrow on top space plus space CA with rightwards arrow on top space equals space 0 with rightwards arrow on top
therefore space space space space ABC space is space straight a space triangle.
space Let space straight D comma space straight E comma space straight F space be space mid minus points space of space sides space BC comma space CA comma space AB space respectively.

    ∴   position vectors of D, E, F are fraction numerator straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction comma space fraction numerator straight c with rightwards arrow on top plus straight a with rightwards arrow on top over denominator 2 end fraction comma space fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top over denominator 2 end fraction respectively.
               AD with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A space equals space fraction numerator straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction minus straight a with rightwards arrow on top
                     equals space 1 half left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top minus 2 space straight a with rightwards arrow on top right parenthesis
equals space 1 half left parenthesis negative stack straight i space with hat on top plus space 3 space straight j with hat on top space plus space 4 space straight k with hat on top space plus space 4 space straight i with hat on top space minus space 2 space straight j with hat on top space minus space 6 space straight k with hat on top space minus space space 6 space straight i with hat on top space minus space 2 space straight j with hat on top space plus space 4 space straight k with hat on top right parenthesis
equals space 1 half left parenthesis negative 3 space straight i with hat on top space minus space straight j with hat on top space plus space 2 space straight k with hat on top right parenthesis
     BE with rightwards arrow on top space equals space straight P. straight V. space of space straight E space minus space straight P. straight V. space of space straight B space equals space fraction numerator straight c with rightwards arrow on top plus straight a with rightwards arrow on top over denominator 2 end fraction minus straight b with rightwards arrow on top
space space space space space space space equals space 1 half left parenthesis straight c with rightwards arrow on top plus straight a with rightwards arrow on top space minus space 2 space straight b with rightwards arrow on top right parenthesis
space space space space space space equals space 1 half left parenthesis 4 space straight i with hat on top space minus space 2 space straight j with hat on top space minus space 6 space straight k with hat on top space plus space 3 space straight i with hat on top space plus space straight j with hat on top space minus space 2 space straight k with hat on top space plus space 2 space straight j with hat on top space minus space 6 space straight j with hat on top space minus space 8 space straight k with hat on top right parenthesis
space space space space space space equals space 1 half left parenthesis 9 space straight i with hat on top space minus space space 7 space straight j with hat on top space minus space 16 space straight k with hat on top right parenthesis
    CF with rightwards arrow on top space equals space straight P. straight V. space of space straight F space minus space straight P. straight V. space of space straight C space equals space fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top over denominator 2 end fraction space minus straight c with rightwards arrow on top
space space space space space space equals space 1 half left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top minus 2 straight c with rightwards arrow on top right parenthesis
space space space space space equals space 1 half left parenthesis 3 space straight i with hat on top space plus space straight j with hat on top space minus space 2 space straight k with hat on top space minus space straight i with hat on top space plus space 3 space straight j with hat on top space plus space 4 space straight k with hat on top space minus space 8 space straight i with hat on top space plus space 4 space straight j with hat on top space plus space 12 space straight k with hat on top right parenthesis
space space space space equals space 1 half left parenthesis negative 6 space straight i with hat on top space plus space 8 space straight j with hat on top space plus space 14 space straight k with hat on top right parenthesis
space space space space equals space minus space 3 space straight i with hat on top space plus space 4 space straight j with hat on top space plus space 7 space straight k with hat on top
    therefore space space space AD space equals space 1 half square root of 9 plus 1 plus 4 end root space equals 1 half square root of 14
space space space space space space space space BE space equals space 1 half square root of 81 plus 49 plus 256 end root space equals 1 half square root of 386
space space space space space space space space CF space equals space square root of 9 plus 16 plus 49 end root space equals square root of 74
    Question 377
    CBSEENMA12034053

    Evaluate the scalar product:
    left parenthesis 3 straight a with rightwards arrow on top space minus space 5 space straight b with rightwards arrow on top right parenthesis. space space left parenthesis 2 straight a with rightwards arrow on top plus space 7 straight b with rightwards arrow on top right parenthesis

    Solution

    Consider left parenthesis 3 straight a with rightwards arrow on top space minus space space 5 straight b with rightwards arrow on top right parenthesis. space left parenthesis 2 straight a with rightwards arrow on top space plus space 7 straight b with rightwards arrow on top right parenthesis
                              equals space 6 space straight a with rightwards arrow on top. space straight a with rightwards arrow on top space plus space 21 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space minus space 10 space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space minus space 35 space straight b with rightwards arrow on top. space straight b with rightwards arrow on top
                               equals space 6 space straight a with rightwards arrow on top squared space plus 21 space straight a with rightwards arrow on top semicolon space straight b with rightwards arrow on top space minus space 10 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space minus 35 space straight b with rightwards arrow on top squared
space equals 6 space open vertical bar straight a with rightwards arrow on top close vertical bar squared space plus space 11 space straight a with rightwards arrow on top. space space straight b with rightwards arrow on top space minus space 35 space open vertical bar straight b with rightwards arrow on top close vertical bar squared space space space space space space space space space space space space space space space space space space space open square brackets because space straight a with bar on top. space straight b with bar on top space equals space straight b with bar on top. space straight a with bar on top close square brackets

    Question 378
    CBSEENMA12034054

    Find open parentheses straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top close parentheses. space space open parentheses 3 space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close parentheses when
        straight a with rightwards arrow on top space equals space straight i with hat on top space minus space 2 space straight j with hat on top space plus space 5 space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space straight j with hat on top space minus space space 3 space straight k with hat on top

    Solution

    Here, 
                    straight a with rightwards arrow on top space equals space straight i with hat on top space minus space 2 space straight j with hat on top space plus space 5 space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space straight j with hat on top space minus space 3 space straight k with hat on top
    therefore space space space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top space equals space left parenthesis 2 space straight i with hat on top space plus space straight j with hat on top space minus space 3 space straight k with hat on top right parenthesis space minus space left parenthesis straight i with hat on top space minus space 2 space straight j with hat on top space plus space 5 space straight k with hat on top right parenthesis space equals space straight i with hat on top space plus space 3 space straight j with hat on top space minus space 8 space straight k with hat on top
          3 straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space equals space left parenthesis 3 space straight i with hat on top space minus space 6 space straight j with hat on top space plus space 15 space straight k with hat on top right parenthesis space plus space left parenthesis 2 straight i with hat on top space plus space straight j with hat on top space minus space 3 space straight k with hat on top right parenthesis space equals space 5 space straight i with hat on top minus space 5 space straight j with hat on top space plus space 12 space straight k with hat on top
    therefore space space space space left parenthesis straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top right parenthesis. space space left parenthesis 3 space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis space equals space left parenthesis straight i with hat on top space plus space 3 space straight j with hat on top space minus space 8 space straight k with hat on top right parenthesis. space left parenthesis 5 straight i with hat on top space minus space 5 straight j with hat on top space plus space 12 space straight k with hat on top right parenthesis
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space left parenthesis 1 right parenthesis thin space left parenthesis 5 right parenthesis space plus space left parenthesis 3 right parenthesis space left parenthesis negative 5 right parenthesis plus space left parenthesis negative 8 right parenthesis thin space left parenthesis 12 right parenthesis
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space 5 minus 15 minus 96
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space minus 106 space space space space space space space space space space space space space space space space space space space space

    Question 379
    CBSEENMA12034055

    Given two points A and B, identify the set of points P in space such that PA with rightwards arrow on top. space PB with rightwards arrow on top space less than space 0.

    Solution

    We have
                      PA with rightwards arrow on top. space PB with rightwards arrow on top space less than space 0
     therefore space space left parenthesis PA right parenthesis space left parenthesis PB right parenthesis space space cos space angle APB space equals space 0
rightwards double arrow space space space cos space angle APB thin space less than thin space 0 space space space space space space space space space space space space space space open square brackets because PA greater than 0 comma space PB greater than 0 close square brackets
rightwards double arrow space space space angle APB space is space obtuse space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis

    Draw a sphere with O as centre and AB as diameter. Take any point P in the interior of this sphere and join PA and PB. It is clear that P is an interior point of the sphere if and only if ∠APB is obtuse.
    ∴  from (1), it follows that the required set of points is the interior of the sphere with AB as a diameter.

    Question 380
    CBSEENMA12034056
    Question 381
    CBSEENMA12034057

    If straight a with rightwards arrow on top is the unit vector and open parentheses straight x with rightwards arrow on top minus straight a with rightwards arrow on top close parentheses. space left parenthesis straight x with rightwards arrow on top space plus space straight a with rightwards arrow on top right parenthesis space equals space 8 comma then find open vertical bar straight x with rightwards arrow on top close vertical bar.

    Solution

    Since straight a with rightwards arrow on top is a unit vector
                         open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 1                                               ...(1)
    Now,    left parenthesis straight x with rightwards arrow on top minus straight a with rightwards arrow on top right parenthesis. space left parenthesis straight x with rightwards arrow on top plus straight a with rightwards arrow on top right parenthesis space equals space 8 space space space space rightwards double arrow space space space straight x with rightwards arrow on top. space straight x with rightwards arrow on top space plus space straight x with rightwards arrow on top. space straight a with rightwards arrow on top space minus space straight a with rightwards arrow on top. space straight x with rightwards arrow on top space minus space straight a with rightwards arrow on top. space straight a with rightwards arrow on top space equals space 8
    therefore space space open vertical bar straight x with rightwards arrow on top close vertical bar squared plus space straight x with rightwards arrow on top. space straight a with rightwards arrow on top space minus space straight x with rightwards arrow on top. space straight a with rightwards arrow on top space minus space open vertical bar straight a with rightwards arrow on top close vertical bar squared space equals space 8 space space space space space space space space space space space space space space space space space space space left square bracket because space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals straight b with rightwards arrow on top. space straight a with rightwards arrow on top right square bracket
therefore space space space open vertical bar straight x with rightwards arrow on top close vertical bar squared space minus space left parenthesis 1 right parenthesis squared space equals 8 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
rightwards double arrow space space space space open vertical bar straight x with rightwards arrow on top close vertical bar squared space equals space 9 space space space space space space space space space rightwards double arrow space space space space space open vertical bar straight x with rightwards arrow on top close vertical bar space equals space 3

    Question 382
    CBSEENMA12034058
    Question 383
    CBSEENMA12034059
    Question 384
    CBSEENMA12034060

    Find the angle between the vectors straight i with hat on top space minus space 2 space straight j with hat on top space plus space 3 space straight k with hat on top space and space 3 space straight i with hat on top space minus space 2 space straight j with hat on top space plus space straight k with hat on top.

    Solution
    Let straight theta be the angle between vectors
                  straight a with rightwards arrow on top space equals space straight i with hat on top space minus space 2 space straight j with hat on top space plus space 3 space straight k with hat on top space space and space straight b with rightwards arrow on top space equals space 3 space straight i with hat on top space minus space 2 space straight j with hat on top space plus space straight k with hat on top
    Now,  straight a space equals space square root of 1 plus 4 plus 9 end root space equals square root of 14 comma space space space straight b space equals space square root of 9 plus 4 plus 1 end root space equals space square root of 14
                    straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space left parenthesis 1 right parenthesis thin space left parenthesis 3 right parenthesis space plus space left parenthesis negative 2 right parenthesis thin space left parenthesis negative 2 right parenthesis space plus space left parenthesis 3 right parenthesis thin space left parenthesis 1 right parenthesis space equals space 3 plus 4 plus 3 space equals space 0
    Now straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space straight a space straight b space cos space straight theta space space space rightwards double arrow space space space space 10 space equals space left parenthesis square root of 14 right parenthesis thin space left parenthesis square root of 14 right parenthesis space cos space straight theta
    therefore space space space space space space space cos space straight theta space equals space 10 over 14 space equals space 5 over 7 space space space space rightwards double arrow space space space space straight theta space equals space cos to the power of negative 1 end exponent open parentheses 5 over 7 close parentheses
    Question 385
    CBSEENMA12034061
    Question 386
    CBSEENMA12034062

    If straight a with rightwards arrow on top space equals space straight i with hat on top plus space 2 space straight j with hat on top space space minus space 3 space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space 3 space straight i with hat on top space minus space straight j with hat on top space plus space 2 space straight k with hat on top comma space space show that open parentheses straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close parentheses space and space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis are perpendicular to each other. 

    Solution
    straight a with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top space minus space 3 space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space 3 space straight i with hat on top space minus space straight j with hat on top space plus space 2 space straight k with hat on top
therefore space space space space space space space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space equals space 4 space straight i with hat on top space plus space straight j with hat on top space minus space straight k with hat on top comma space space space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space equals space minus 2 space straight i with hat on top space plus space 3 space straight j with hat on top space minus space 5 space straight k with hat on top
    Now,    open parentheses straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close parentheses space. space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space equals space 4 space left parenthesis negative 2 right parenthesis space plus space left parenthesis 1 right parenthesis thin space left parenthesis 3 right parenthesis thin space plus space left parenthesis negative 1 right parenthesis thin space left parenthesis negative 5 right parenthesis space space space
                                                 equals negative 8 plus 3 plus 5
equals space 0
    therefore space space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space space and space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top are perpendicular to each other. 
    Question 387
    CBSEENMA12034063

    If straight a with rightwards arrow on top space equals space 5 space straight i with hat on top space minus space straight j with hat on top space minus space space 3 space straight k with hat on top space and space straight b with rightwards arrow on top space equals space straight i with hat on top plus 3 space straight j with hat on top space minus space 5 space straight k with hat on top comma space then show that the vectors straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space and space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space are space orthogonal.

    Solution

           straight a with rightwards arrow on top space equals space 5 space straight i with hat on top space minus space straight j with hat on top space minus space 3 space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space straight i with hat on top space plus space 3 space straight j with hat on top space minus space 5 space straight k with hat on top
    therefore space space space space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space equals space 6 space straight i with hat on top space plus space 2 space straight j with hat on top space minus space 8 space straight k with hat on top comma space space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space equals space 4 space straight i with hat on top space minus space 4 space straight j with hat on top space plus space 2 space straight k with hat on top
    left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space equals space left parenthesis 6 right parenthesis thin space left parenthesis 4 right parenthesis space plus space left parenthesis 2 right parenthesis thin space left parenthesis 4 right parenthesis space plus space left parenthesis negative 8 right parenthesis thin space left parenthesis 2 right parenthesis
                          equals space 24 minus 8 minus 16 space equals space 0
    therefore space space space straight a with rightwards arrow on top plus straight b with rightwards arrow on top space and space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space are space orthogonal space vectors. space

    Question 388
    CBSEENMA12034064

    For what values of A are the vectors 
    straight a with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space straight lambda space straight j with hat on top space plus space straight k with hat on top space and space straight b with rightwards arrow on top space equals space straight i with hat on top space minus space 2 space straight j with hat on top space plus space 3 space straight k with hat on top perpendicular to each other?

    Solution
    Here
              straight a with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space straight lambda space straight j with hat on top space plus space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space straight i with hat on top space minus space 2 space straight j with hat on top space plus space 3 space straight k with hat on top
                        straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space left parenthesis 2 right parenthesis space left parenthesis 1 right parenthesis space plus space left parenthesis straight lambda right parenthesis space left parenthesis negative 2 right parenthesis space plus space left parenthesis 1 right parenthesis thin space left parenthesis 3 right parenthesis space equals space 2 space minus space 2 space straight lambda space plus space 3 space equals space minus 2 space straight lambda space plus space 5
    because space space space space space straight a with rightwards arrow on top space and space straight b with rightwards arrow on top space are space perpendicular space to space each space other
therefore space space space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0 space space space rightwards double arrow space space space minus 2 straight lambda space plus 5 space equals space space 0 space space space rightwards double arrow space space space 2 space straight lambda space equals 5
therefore space space space space space space space space space space straight lambda space equals space 5 over 2
    Question 389
    CBSEENMA12034065

    If straight a with rightwards arrow on top space equals space 3 straight i with hat on top space plus space 2 straight j with hat on top space plus space 9 straight k with hat on top space and space straight b with rightwards arrow on top space equals space straight i with hat on top space plus space straight lambda straight j with hat on top space plus space 3 straight k with hat on top comma find the value of straight lambda so that straight a with rightwards arrow on top plus straight b with rightwards arrow on top is perpendicular to straight a with rightwards arrow on top minus straight b with rightwards arrow on top.

    Solution

              straight a with rightwards arrow on top space equals space 3 straight i with hat on top space plus space 2 straight j with hat on top space plus space 9 straight k with hat on top comma space space space space straight b with rightwards arrow on top space equals space straight i with hat on top space plus space straight lambda straight j with hat on top space plus space 3 straight k with hat on top
    therefore space space space straight a with rightwards arrow on top plus straight b with rightwards arrow on top space equals space 4 straight i with hat on top plus left parenthesis straight lambda plus 2 right parenthesis space straight j with hat on top plus 12 straight k with hat on top comma space space straight a with rightwards arrow on top minus straight b with rightwards arrow on top space equals space 2 space straight i with hat on top plus space left parenthesis 2 minus space straight lambda right parenthesis space straight j with hat on top space plus space 6 straight k with hat on top space
    Since straight a with rightwards arrow on top plus straight b with rightwards arrow on top is perpendicular to straight a with rightwards arrow on top minus straight b with rightwards arrow on top
    therefore space space space space space space space space space space space space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top space minus straight b with rightwards arrow on top right parenthesis space equals space 0
therefore space space space space space space left parenthesis 4 right parenthesis thin space left parenthesis 2 right parenthesis space plus space left parenthesis straight lambda plus 2 right parenthesis thin space left parenthesis 2 minus straight lambda right parenthesis space plus space left parenthesis 12 right parenthesis thin space left parenthesis 6 right parenthesis equals space 0
therefore space space space space 8 plus 4 minus straight lambda squared plus 72 space equals 0 space space space rightwards double arrow space space space space straight lambda squared space equals space 84 space space space space rightwards double arrow space space space straight lambda space equals space plus-or-minus square root of 84 space equals plus-or-minus square root of 4 cross times 21 end root
therefore space space space space space space space straight lambda space equals plus-or-minus 2 square root of 21

    Question 390
    CBSEENMA12034066

    Let straight a with rightwards arrow on top space equals space 5 straight i with hat on top space minus space straight j with hat on top space plus space 7 straight k with hat on top and straight b with rightwards arrow on top space equals straight i with hat on top minus straight j with hat on top plus straight lambda straight k with hat on top. Find straight lambda such that straight a with rightwards arrow on top plus straight b with rightwards arrow on top and straight a with rightwards arrow on top minus straight b with rightwards arrow on top are orthogonal .

    Solution

       straight a with rightwards arrow on top space equals space 5 straight i with hat on top minus straight j with hat on top plus 7 straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space straight i with hat on top minus straight j with hat on top plus straight lambda straight k with hat on top
    therefore space space straight a with rightwards arrow on top plus straight b with rightwards arrow on top space equals 6 space straight i with hat on top space minus 2 space straight j with hat on top space plus left parenthesis straight lambda plus 7 right parenthesis space straight k with hat on top comma space space straight a with rightwards arrow on top minus straight b with rightwards arrow on top space equals 4 space straight i with hat on top plus left parenthesis 7 minus straight lambda right parenthesis space straight k with hat on top
    Since straight a with rightwards arrow on top plus straight b with rightwards arrow on top space and space straight a with rightwards arrow on top space minus straight b with rightwards arrow on top are orthogonal
    therefore space space space space left parenthesis straight a with rightwards arrow on top space plus straight b with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space equals space 0
therefore space space space space left parenthesis 6 right parenthesis left parenthesis 4 right parenthesis plus left parenthesis negative 2 right parenthesis left parenthesis 0 right parenthesis plus left parenthesis 7 plus straight lambda right parenthesis space left parenthesis 7 minus straight lambda right parenthesis space equals space 0
therefore space space space 24 plus 49 minus straight lambda squared space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space rightwards double arrow space straight lambda squared space equals space 73
therefore space space space space space space space space straight lambda space equals plus-or-minus square root of 73

    Question 391
    CBSEENMA12034067

    Find straight lambda if the vectors 5 straight i with hat on top plus 2 straight j with hat on top minus straight k with hat on top and straight lambda straight i with hat on top space minus space straight j with hat on top space plus space 5 space straight k with hat on top are orthogonal.

    Solution

    Let straight a with rightwards arrow on top space equals space 5 straight i with hat on top plus 2 straight j with hat on top space minus straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space straight lambda straight i with hat on top space minus space straight j with hat on top space plus space 5 space straight k with hat on top
            straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space left parenthesis 5 right parenthesis thin space left parenthesis straight lambda right parenthesis plus left parenthesis 2 right parenthesis thin space left parenthesis negative 1 right parenthesis space plus space left parenthesis negative 1 right parenthesis space left parenthesis 5 right parenthesis space equals space 5 space straight lambda minus 2 minus 5 space equals 5 straight lambda minus 7
    because space space space space straight a with rightwards arrow on top space and space straight b with rightwards arrow on top space are space orthogonal
therefore space space space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space rightwards double arrow space space 5 space straight lambda space minus space 7 space equals space 0 space space space space space rightwards double arrow space space space straight lambda space equals space 7 over 5.

    Question 392
    CBSEENMA12034068

    If straight a with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space 2 space straight j with hat on top space plus space 3 space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals negative straight i with hat on top space plus space 2 space straight j with hat on top space plus space straight k with hat on top space space and space straight c with rightwards arrow on top space equals 3 straight i with hat on top space plus space straight j with hat on top such that straight a with rightwards arrow on top space plus space straight lambda straight b with rightwards arrow on top is perpendicular to straight c with rightwards arrow on top, then find the value of straight lambda.

    Solution

             straight a with rightwards arrow on top space equals 2 space straight i with hat on top space plus space 2 space straight j with hat on top space plus space 3 space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space minus straight i with hat on top space plus space 2 space straight j with hat on top space plus space straight k with hat on top comma space space straight c with rightwards arrow on top space equals space 3 space straight i with hat on top space plus space straight j with hat on top
    therefore space space space space straight a with rightwards arrow on top space plus space straight lambda straight b with rightwards arrow on top space equals space left parenthesis 2 space minus space straight lambda right parenthesis straight i with hat on top space plus space 2 space left parenthesis 1 space plus straight lambda right parenthesis space straight j with hat on top space plus left parenthesis 3 plus straight lambda right parenthesis space straight k with hat on top
    Since straight a with rightwards arrow on top plus straight lambda straight b with rightwards arrow on top is perpendicular to straight c with rightwards arrow on top
    therefore space space space left parenthesis straight a with rightwards arrow on top space plus space straight lambda straight b with rightwards arrow on top right parenthesis. space straight c with rightwards arrow on top space equals space 0
    therefore space space space space left parenthesis 2 minus straight lambda right parenthesis space left parenthesis 3 right parenthesis space plus space 2 space left parenthesis 1 plus straight lambda right parenthesis space left parenthesis 1 right parenthesis space plus space left parenthesis 3 space plus straight lambda right parenthesis space left parenthesis 0 right parenthesis space equals 0
therefore space space space space space 6 minus 3 straight lambda space plus 2 space plus space 2 straight lambda space equals space 0 space space space space space space space space rightwards double arrow space space space space space space straight lambda space equals space 8.

    Question 393
    CBSEENMA12034069

    Find the value of A such that the vectors 3 straight a with rightwards arrow on top plus space 4 straight b with rightwards arrow on top and 2 straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top are perpendicular to each other when 

    Solution

            straight a with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top space minus space 3 space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space straight i with hat on top space plus space straight lambda space straight j with hat on top space plus space space 5 space straight k with hat on top.
    Here,  straight a with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top space minus space 3 space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space straight i with hat on top space plus space straight lambda space straight j with hat on top space plus space 5 space straight k with hat on top
    therefore space space space 3 space straight a with rightwards arrow on top space plus space 4 space straight b with rightwards arrow on top space equals space 3 space left parenthesis straight i with hat on top space plus space 2 space straight j with hat on top space minus space 3 space straight k with hat on top right parenthesis plus space 4 space left parenthesis straight i with hat on top space plus space straight lambda space straight j with hat on top space plus space 5 space straight k with hat on top right parenthesis
                                  equals 7 straight i with hat on top plus left parenthesis 6 plus 4 straight lambda right parenthesis straight j with hat on top space plus 11 space straight k with hat on top
    and 2 straight a with rightwards arrow on top plus straight b with rightwards arrow on top space equals space 2 left parenthesis straight i with hat on top plus 2 straight j with hat on top space minus 3 straight k with hat on top right parenthesis space plus space left parenthesis straight i with hat on top plus straight lambda straight j with hat on top space plus space 5 straight k with hat on top right parenthesis
                         equals space 3 straight i with hat on top plus left parenthesis 4 plus straight lambda right parenthesis straight j with hat on top space minus space straight k with hat on top
    Since 3 straight a with rightwards arrow on top plus space 4 straight b with rightwards arrow on top space and space 2 straight a with rightwards arrow on top plus straight b with rightwards arrow on top are perpendicular to each other
     therefore space space space left parenthesis 3 straight a with rightwards arrow on top space plus space 4 straight b with rightwards arrow on top right parenthesis. space left parenthesis 2 straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space equals space 0
therefore space space space left curly bracket 7 straight i with hat on top plus left parenthesis 6 plus 4 straight lambda right parenthesis space straight j with hat on top space plus space 11 space straight k with hat on top right curly bracket. space open curly brackets 3 straight i with hat on top space plus left parenthesis 4 plus straight lambda right parenthesis space straight j with hat on top space minus space straight k with hat on top close curly brackets space equals space 0
therefore space left parenthesis 7 right parenthesis thin space left parenthesis 3 right parenthesis space plus space left parenthesis 6 plus 4 space straight lambda right parenthesis space left parenthesis 4 plus straight lambda right parenthesis plus left parenthesis 11 right parenthesis thin space left parenthesis negative 1 right parenthesis space equals space 0
therefore space space space 21 plus 24 plus 22 straight lambda space plus space 4 straight lambda squared minus 11 space equals space 0
therefore space space space 4 straight lambda squared space plus 22 straight lambda space plus 34 space equals space 0
rightwards double arrow space space space 2 straight lambda squared plus 11 straight lambda plus 22 space equals space 0
therefore space space space straight lambda space equals space fraction numerator negative 11 plus-or-minus square root of 121 minus 176 end root over denominator 4 end fraction equals space fraction numerator negative 11 plus-or-minus square root of negative 55 end root over denominator 2 end fraction
    there exist no real value of A.

    Question 394
    CBSEENMA12034070

    If open vertical bar straight a with rightwards arrow on top close vertical bar space equals space square root of 3 comma space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 2 space and space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 3 comma find the angle between straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.

    Solution
    open vertical bar straight a with rightwards arrow on top close vertical bar space equals space square root of 3 comma space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 2 comma space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space space equals 3
      Let straight theta be angle between straight a with rightwards arrow on top space and space straight b with rightwards arrow on top
      Now,         straight a with rightwards arrow on top. space space straight b with rightwards arrow on top space equals space 3 space space space space space space space rightwards double arrow space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar space cos space straight theta space equals space 3
    therefore space space space left parenthesis square root of 3 right parenthesis thin space left parenthesis 2 right parenthesis space cos space straight theta space equals space 3 space space space space space space rightwards double arrow space space space cos space straight theta space equals fraction numerator square root of 3 over denominator 2 end fraction
therefore space space space space space space space straight theta space equals space 30 degree
    Question 395
    CBSEENMA12034071

    Find the angle between two vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top with magnitude 1 and 2 respectively and such that straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 1

    Solution

    Here, 
    a = 1,   b = 2,  straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 1
    Let straight theta be the angle between two vectors.
    Now,             straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 1 space space space space space space rightwards double arrow space space ab space cos space straight theta space equals space 1 space space space space rightwards double arrow space space space left parenthesis 1 right parenthesis thin space left parenthesis 2 right parenthesis space cos space straight theta space equals space 1
    therefore space space cos space straight theta space equals space 1 half space space space space space space rightwards double arrow space space space straight theta space equals space 60 degree

    Question 396
    CBSEENMA12034072

    If straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are two vectors such that open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 4 comma space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 3 space space and space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space equals space 6 find the angle between straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.

    Solution

    Here open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 4 comma space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 3 space and space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 6
    Let straight theta be angle between straight a with rightwards arrow on top space and space straight b with rightwards arrow on top space equals space 6.
    Now, straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar space cos space straight theta space space space space space space space space space space space rightwards double arrow space space space space 6 space equals space left parenthesis 4 right parenthesis thin space left parenthesis 3 right parenthesis space cos space straight theta
    rightwards double arrow space space space space cos space straight theta space equals space 1 half space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space rightwards double arrow space space space space straight theta space equals space 60 degree

    Question 397
    CBSEENMA12034073

    Find the angle between two vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top with magnitudes 2  and 1 respectively, and such that straight a with rightwards arrow on top space. space straight b with rightwards arrow on top space equals space square root of 3.

    Solution

    Here a = 2,    b = 1,   straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space square root of 3
    Let straight theta be angle between straight a with rightwards arrow on top space and space straight b with rightwards arrow on top
    Now,
                 straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space ab space cos space straight theta space space space space space space space space space space space space space space space space space space space space space rightwards double arrow space space space space square root of 3 space equals space left parenthesis 2 right parenthesis thin space left parenthesis 1 right parenthesis space space cos space straight theta
therefore space space space space cos space straight theta space equals space fraction numerator square root of 3 over denominator 2 end fraction space space space space space space space space space space space space space space space space rightwards double arrow space space space straight theta space equals space 30 degree space. space space space space space

    Question 398
    CBSEENMA12034074

    Find the angle between two vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top with magnitudes square root of 3 space and space 2 comma space respectively comma space and space that space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space square root of 6.

    Solution

    Here straight a equals space square root of 3 comma space space straight b space equals space 2 comma space space straight a with rightwards arrow on top space. space straight b with rightwards arrow on top space equals space square root of 6
    Let straight theta be the angle between and straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.
    Now,   straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space ab space cos space straight theta space space space space space space space space space space space space space space space rightwards double arrow space space space space square root of 6 space equals space left parenthesis square root of 3 right parenthesis thin space left parenthesis 2 right parenthesis space cos space straight theta
    rightwards double arrow space space space cos space straight theta space equals space fraction numerator square root of 6 over denominator 2 square root of 3 end fraction space equals space fraction numerator 1 over denominator square root of 2 end fraction space space space space rightwards double arrow space space space space straight theta space equals space 45 degree

    Question 399
    CBSEENMA12034075

    straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are two vectors such that open vertical bar straight a with rightwards arrow on top close vertical bar space equals 2 comma space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 3 space and space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 3 comma find the angle between straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.

    Solution

    We have open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 2 comma space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 3 comma space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 3
    Let straight theta be the angle between straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.
    therefore space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar space cos space straight theta space space space space space rightwards double arrow space space space 3 space equals space left parenthesis 2 right parenthesis thin space left parenthesis 3 right parenthesis space cos space straight theta
therefore space space space space cos space straight theta space equals space 1 half space space space space space rightwards double arrow space space space space straight theta space equals space 60 degree

    Question 400
    CBSEENMA12034076
    Question 401
    CBSEENMA12034077

    Find the angle between two vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top such that open vertical bar straight a with rightwards arrow on top close vertical bar space equals space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 3 and straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 1.

    Solution

    Here open vertical bar straight a with rightwards arrow on top close vertical bar = open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 3 comma space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 1
    Let straight theta be the angle between straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.
    Now,
               straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space ab space cos space straight theta space space space space space space space space space space space space space space space rightwards double arrow space space space space 1 space equals space left parenthesis 3 right parenthesis thin space left parenthesis 3 right parenthesis space cos space straight theta
rightwards double arrow space space space cos space straight theta space equals space 1 over 9 space space space space space space space space space space space space space space space space rightwards double arrow space space straight theta space equals space cos to the power of negative 1 end exponent open parentheses 1 over 9 close parentheses

    Question 402
    CBSEENMA12034078

    Find the magnitude of two vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top having the same magnitude and such that the angle between them is 30° and their scalar product is 3.

    Solution

    Let straight theta be angle between straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.
    therefore space space space straight theta space equals space 30 degree comma space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space open vertical bar straight b with rightwards arrow on top close vertical bar comma space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 3                              ...(1)
    Now,              straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 3 space space space space rightwards double arrow space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar space cos space 30 degree space equals space 3
    rightwards double arrow space space space open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight a with rightwards arrow on top close vertical bar space cross times fraction numerator square root of 3 over denominator 2 end fraction space equals space 3 space space space space space rightwards double arrow space space space open vertical bar straight a with rightwards arrow on top close vertical bar squared space equals space 2 square root of 3 space equals space 3.46 space space space space space space left square bracket because space of space left parenthesis 1 right parenthesis right square bracket
therefore space space space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 1.86 space equals space open vertical bar straight b with rightwards arrow on top close vertical bar

    Question 403
    CBSEENMA12034079
    Question 404
    CBSEENMA12034080

    Find open vertical bar straight a with rightwards arrow on top close vertical bar and open vertical bar straight b with rightwards arrow on top close vertical bar comma if  open parentheses straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close parentheses. space left parenthesis straight a with rightwards arrow on top space minus straight b with rightwards arrow on top right parenthesis space equals space 12 space and space open vertical bar straight a with rightwards arrow on top close vertical bar space equals 2 space open vertical bar straight b with rightwards arrow on top close vertical bar.

    Solution

    We have
            left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis space equals space 12
    therefore space space space space open vertical bar straight a with rightwards arrow on top close vertical bar squared minus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space 12
rightwards double arrow space space space space left parenthesis 2 space open vertical bar straight b with rightwards arrow on top close vertical bar right parenthesis squared space minus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space 12 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 2 space open vertical bar straight b with rightwards arrow on top close vertical bar close square brackets
rightwards double arrow space space space space 4 space open vertical bar straight b with rightwards arrow on top close vertical bar squared space minus open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals 12 space space space space space space space space rightwards double arrow space space 3 space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space 12
therefore space space space space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space 4 space space space space space space space space space space space space space space space space space rightwards double arrow space space space space open vertical bar straight b with rightwards arrow on top close vertical bar space space equals space 2
therefore space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 2 space cross times 2 space equals space 4 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 2 space open vertical bar straight b with rightwards arrow on top close vertical bar close square brackets space space

    Question 405
    CBSEENMA12034081

    Find open vertical bar straight a with rightwards arrow on top close vertical bar space and space space open vertical bar straight b with rightwards arrow on top close vertical bar space if space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space equals space 8 space space and space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 8 space open vertical bar straight b with rightwards arrow on top close vertical bar.

    Solution

      left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space equals space 8 space space space space rightwards double arrow space space space open vertical bar straight a with rightwards arrow on top close vertical bar squared minus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals 8
    rightwards double arrow space space 64 space open vertical bar straight b with rightwards arrow on top close vertical bar squared space minus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space 8                                                        open square brackets because space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 8 space open vertical bar straight b with rightwards arrow on top close vertical bar close square brackets
    rightwards double arrow space space space space 63 space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space 8 space space space space space space space space space space rightwards double arrow space space space space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space 8 over 63 space space space space space space space rightwards double arrow open vertical bar straight b with rightwards arrow on top close vertical bar space equals fraction numerator 2 square root of 2 over denominator square root of 63 end fraction
therefore space space space space space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals 8 space cross times space fraction numerator 2 space square root of 2 over denominator square root of 63 end fraction space equals fraction numerator 16 space square root of 2 over denominator square root of 63 end fraction

    Question 406
    CBSEENMA12034082

    Find open vertical bar straight a with rightwards arrow on top close vertical bar space and space open vertical bar straight b with rightwards arrow on top close vertical bar space if space space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. thin space left parenthesis straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis space equals 3 space and space 2 space open vertical bar straight b with rightwards arrow on top close vertical bar space equals open vertical bar straight a with rightwards arrow on top close vertical bar.

    Solution

       left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis space equals space 3 space space space space space rightwards double arrow space space space space open vertical bar straight a with rightwards arrow on top close vertical bar squared minus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space 3
    rightwards double arrow space space space 4 space open vertical bar straight b with rightwards arrow on top close vertical bar squared space minus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space 3 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 2 space open vertical bar straight b with rightwards arrow on top close vertical bar close square brackets
rightwards double arrow space space space 3 space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space 3 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space rightwards double arrow space space space space space space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals 1
therefore space space space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 1 comma space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 2 space cross times 1 space equals space 2.

    Question 407
    CBSEENMA12034083

    If left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis space equals 0 show that open vertical bar straight a with rightwards arrow on top close vertical bar space equals open vertical bar straight b with rightwards arrow on top close vertical bar

    Solution
    because space space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis space equals space 0
    therefore space space space straight a with rightwards arrow on top squared space equals space straight b with rightwards arrow on top squared comma space space space space or space space space open vertical bar straight a with rightwards arrow on top close vertical bar squared space equals space open vertical bar straight b with rightwards arrow on top close vertical bar squared space space space space rightwards double arrow space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space open vertical bar straight b with rightwards arrow on top close vertical bar
    Question 409
    CBSEENMA12034085

    Prove that open vertical bar straight a with rightwards arrow on top close vertical bar space straight b with rightwards arrow on top space plus space open vertical bar straight b with rightwards arrow on top close vertical bar space straight a with rightwards arrow on top is orthogonal to open vertical bar straight a with rightwards arrow on top close vertical bar space straight b with rightwards arrow on top space minus space open vertical bar straight b with rightwards arrow on top close vertical bar space straight a with rightwards arrow on top, for any vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.

    Solution
    left parenthesis open vertical bar straight a with rightwards arrow on top close vertical bar space straight b with rightwards arrow on top space plus space open vertical bar straight b with rightwards arrow on top close vertical bar space straight a with rightwards arrow on top right parenthesis. space space open parentheses open vertical bar straight a with rightwards arrow on top close vertical bar space straight b with rightwards arrow on top space minus space open vertical bar straight b with rightwards arrow on top close vertical bar space straight a with rightwards arrow on top close parentheses
                                   equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared space straight b with rightwards arrow on top squared space minus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space straight a with rightwards arrow on top squared space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared space open vertical bar straight b with rightwards arrow on top close vertical bar squared space minus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space open vertical bar straight a with rightwards arrow on top close vertical bar squared
equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared space open vertical bar straight b with rightwards arrow on top close vertical bar squared space minus space open vertical bar straight a with rightwards arrow on top close vertical bar squared space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space 0
    therefore space space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space straight b with rightwards arrow on top space plus space open vertical bar straight b with rightwards arrow on top close vertical bar space straight a with rightwards arrow on top space and space open vertical bar straight a with rightwards arrow on top close vertical bar space straight b with rightwards arrow on top space minus space open vertical bar straight b with rightwards arrow on top close vertical bar space straight a with rightwards arrow on top space are space orthozonal space for space any space vectors space straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.
    Question 410
    CBSEENMA12034086

    Prove that
    left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. space open parentheses straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close parentheses space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared
    if and only if straight a with rightwards arrow on top comma space straight b with rightwards arrow on top are orthogonal.

    Solution
    (i) Assume that
               left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared 
    therefore space space space space space space straight a with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space. space straight b with rightwards arrow on top space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared
rightwards double arrow space space space space space open vertical bar straight a with rightwards arrow on top close vertical bar squared space plus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared
rightwards double arrow space space space 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0 space space space space space space space rightwards double arrow space space space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0
rightwards double arrow space space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space are space orthogonal. space
    (ii) Assume that straight a with rightwards arrow on top comma space straight b with rightwards arrow on top  are orthogonal
       therefore space space space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0                                                                  ...(1)
    Now left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space equals space straight a with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight b with rightwards arrow on top
                                equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus 0 plus 0 plus open vertical bar straight b with rightwards arrow on top close vertical bar squared space space space space space space left square bracket because space of space left parenthesis 1 right parenthesis right square bracket
    Now,    left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared
    Hence the result. 
    Question 411
    CBSEENMA12034087

    Let straight a with rightwards arrow on top space and space straight b with rightwards arrow on top be the two non-zero vectors. Then, prove that straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are perpendicular if and only if open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar.

    Solution

    (i) Assume that straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are perpendicular
    therefore space space space space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0                                                    ...(i)
                 open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar squared space equals space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis squared space equals space straight a with rightwards arrow on top squared plus straight b with rightwards arrow on top squared plus 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top
    equals space straight a with rightwards arrow on top squared plus straight b with rightwards arrow on top squared space plus space space 2 space left parenthesis 0 right parenthesis space space space space space space space space space space space space space space open square brackets because space space of space left parenthesis straight i right parenthesis close square brackets
    therefore space space space space open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar squared space equals space straight a with rightwards arrow on top squared plus straight b with rightwards arrow on top squared space                                       ...(2)
    Again,  open vertical bar straight a with rightwards arrow on top minus straight b with rightwards arrow on top close vertical bar squared space equals space left parenthesis straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis squared space equals space straight a with rightwards arrow on top squared plus straight b with rightwards arrow on top squared space minus space 2 straight a with rightwards arrow on top. space straight b with rightwards arrow on top
                                 equals space straight a with rightwards arrow on top squared plus straight b with rightwards arrow on top squared space minus space 2 left parenthesis 0 right parenthesis space space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis straight i right parenthesis close square brackets
    therefore space space space open vertical bar straight a with rightwards arrow on top minus straight b with rightwards arrow on top close vertical bar squared space equals space straight a with rightwards arrow on top squared plus straight b with rightwards arrow on top squared                                         ...(3)
    Fom (2) and (3), we get.
             open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar squared space equals space open vertical bar straight a with rightwards arrow on top space minus straight b with rightwards arrow on top close vertical bar squared
    therefore space space space space space open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar
    (ii) Assume that 
                  open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar
    therefore space space space space open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar squared space equals space open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar squared                                       open square brackets because space space straight a with rightwards arrow on top squared space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared close square brackets
    rightwards double arrow space space space space space straight a with rightwards arrow on top squared plus straight b with rightwards arrow on top squared plus 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space straight a with rightwards arrow on top squared plus straight b with rightwards arrow on top squared space minus space 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top
rightwards double arrow space space space space space space 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space space equals space minus space 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space space space space rightwards double arrow space space space 4 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0
rightwards double arrow space space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0 space space space space rightwards double arrow space space space space straight a with rightwards arrow on top space and space straight b with rightwards arrow on top space are space perpendicular.

    Question 412
    CBSEENMA12034088

    Prove that two vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are perpendicular if 
           open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar squared space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared

    Solution
    because space space space space space open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar squared space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared
therefore space space space space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis squared space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared space plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space open vertical bar straight a with rightwards arrow on top close vertical bar squared space equals space straight a with rightwards arrow on top squared close square brackets
therefore space space space space straight a with rightwards arrow on top squared space plus space straight b with rightwards arrow on top squared space plus space 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space straight a with rightwards arrow on top squared space plus space straight b with rightwards arrow on top squared space space space space rightwards double arrow space space space space 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0 space space space rightwards double arrow space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0
therefore space space space space straight a with rightwards arrow on top space and space straight b with rightwards arrow on top space are space perpendicular.

    Tips: -

    By writing the steps in the reverse order, we can prove that open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar squared space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus open vertical bar straight b with rightwards arrow on top close vertical bar squared only if  straight a with rightwards arrow on top space and space straight b with rightwards arrow on top space are space perpendicular.
    Question 413
    CBSEENMA12034089

    If straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are perpendicular, then left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis squared space equals space left parenthesis straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis squared
     

    Solution
    because space space straight a with rightwards arrow on top space and space straight b with rightwards arrow on top space space are space perpendicular
because space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
    Now open parentheses straight a with rightwards arrow on top plus straight b with rightwards arrow on top close parentheses squared space equals space open parentheses straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close parentheses squared
    If straight a with rightwards arrow on top squared plus straight b with rightwards arrow on top squared space plus 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space straight a with rightwards arrow on top squared plus straight b with rightwards arrow on top squared space minus space 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top
    i.e.,  if 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space minus 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space space straight i. straight e. comma space space if space 4 straight a with rightwards arrow on top. space straight b with rightwards arrow on top
    i.e., if straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0 comma which is true.                                          open square brackets because space if space left parenthesis 1 right parenthesis close square brackets
    Hence the result. 
    Question 414
    CBSEENMA12034090

    If open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 3 comma space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 4 space and space open vertical bar straight c with rightwards arrow on top close vertical bar space equals 5 such that each is perpendicular to sum of the other two, find open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar.

    Solution

    We have
            open vertical bar straight a with rightwards arrow on top close vertical bar space equals 3 comma space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 4 comma space space open vertical bar straight c with rightwards arrow on top close vertical bar space equals space 5                            ...(1)
     Since straight a with rightwards arrow on top is perpendicular to straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top comma space straight b with rightwards arrow on top space is space perp comma space straight c with rightwards arrow on top plus straight a with rightwards arrow on top space and space straight c with rightwards arrow on top space is space perp. space to space straight a with rightwards arrow on top plus straight b with rightwards arrow on top
    therefore space space space straight a with rightwards arrow on top. space left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space equals space straight b with rightwards arrow on top. space space space left parenthesis straight c with rightwards arrow on top space plus space straight a with rightwards arrow on top right parenthesis space equals space straight c with rightwards arrow on top. space left parenthesis straight a with rightwards arrow on top plus space straight b with rightwards arrow on top right parenthesis space equals space 0
therefore space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight c with rightwards arrow on top space equals space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space equals space straight c with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0 space space space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis
    Now,  open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar squared space equals space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis                                
            equals space straight a with rightwards arrow on top. straight a with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top. straight c with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight b with rightwards arrow on top space. straight c with rightwards arrow on top space plus space straight c with rightwards arrow on top. straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight c with rightwards arrow on top
space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared thin space left parenthesis straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight c with rightwards arrow on top right parenthesis space plus space left parenthesis straight b with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight c with rightwards arrow on top right parenthesis space plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space plus left parenthesis straight c with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight b with rightwards arrow on top right parenthesis space plus space open vertical bar straight c with rightwards arrow on top close vertical bar squared
space equals left parenthesis 3 right parenthesis squared plus 0 plus 0 plus left parenthesis 4 right parenthesis squared plus 0 plus left parenthesis 5 right parenthesis squared space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis comma space left parenthesis 2 right parenthesis close square brackets
equals space 9 plus 16 plus 25 space equals space 50
    therefore space space space space open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar space equals space square root of 50 space equals space 5 square root of 2

    Question 415
    CBSEENMA12034091

    Find open vertical bar straight a with rightwards arrow on top minus straight b with rightwards arrow on top close vertical bar comma space if two vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are such that open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 2 comma space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 3 space and space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 4.

    Solution

    Here,  open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 2 comma space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 3 comma space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 4
    Now,  open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar squared space equals space left parenthesis straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space equals space straight a with rightwards arrow on top. space straight a with rightwards arrow on top space minus space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space minus space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top. space straight b with rightwards arrow on top
    equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared space minus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared
equals space left parenthesis 2 right parenthesis squared minus 4 minus 4 plus left parenthesis 3 right parenthesis squared space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
space equals space 4 minus space 4 minus 4 plus 9 space equals space 5
therefore space space space space space space open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar space equals space square root of 5

    Question 416
    CBSEENMA12034092

    Find open vertical bar straight a with rightwards arrow on top minus straight b with rightwards arrow on top close vertical bar comma if open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 2 comma space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 5 space space and space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 8

    Solution

    Here open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 2 comma space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 5 comma space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 8                       ...(1)
    Now,    open vertical bar straight a with rightwards arrow on top minus straight b with rightwards arrow on top close vertical bar squared space equals space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis squared space equals straight a with rightwards arrow on top squared plus straight b with rightwards arrow on top squared space minus space 2 space straight a with rightwards arrow on top. straight b with rightwards arrow on top space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space minus space 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top
                              equals 4 plus 25 minus 16                                    open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
                               equals space 13
    therefore space space space open vertical bar straight a with rightwards arrow on top space minus straight b with rightwards arrow on top close vertical bar space equals space square root of 13

    Question 417
    CBSEENMA12034093

    Find open vertical bar straight a with rightwards arrow on top minus straight b with rightwards arrow on top close vertical bar squared if open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 3 comma space space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 4 space and space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 1.

    Solution

    Here open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 3 comma space space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 4 comma space space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 1                             ...(1)
    Now,         open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar squared space space equals space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis squared space equals space straight a with rightwards arrow on top squared plus space straight b with rightwards arrow on top squared space minus space 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared space plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space minus space 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top
                                equals space 9 plus 16 minus 2 space equals space 23 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space left square bracket because space of space left parenthesis 1 right parenthesis right square bracket

    Question 418
    CBSEENMA12034094

    If straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are unit vectors, and straight theta is the angle between them, find 1 half open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar in terms of straight theta.

    Solution

    We have
          open vertical bar straight a with rightwards arrow on top minus straight b with rightwards arrow on top close vertical bar squared space equals space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis squared space equals space straight a with rightwards arrow on top squared plus straight b with rightwards arrow on top squared space minus space 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top
                         equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space minus space 2 space open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar space cos space straight theta
equals space left parenthesis 1 right parenthesis squared plus left parenthesis 1 right parenthesis squared space minus space 2 left parenthesis 1 right parenthesis thin space left parenthesis 1 right parenthesis space cos space straight theta
                                                open square brackets because space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 1 comma space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 1 space as space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space are space unit space vectors close square brackets
                     equals space 2 left parenthesis 1 minus cos space straight theta right parenthesis space equals space 2 space open parentheses 2 space sin squared space straight theta over 2 close parentheses
    therefore space space space space open vertical bar straight a with rightwards arrow on top space minus straight b with rightwards arrow on top close vertical bar squared space equals space 4 space sin squared space straight theta over 2
therefore space space space space sin space straight theta over 2 space equals 1 half space open vertical bar straight a with rightwards arrow on top minus straight b with rightwards arrow on top close vertical bar space space space space space space space space space space space open square brackets because space space 0 space less or equal than space straight theta space less or equal than space straight pi space space rightwards double arrow space space sin space straight theta over 2 greater or equal than space 0 close square brackets
because space space space space 1 half open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar space equals space sin space straight theta over 2.
        

    Question 419
    CBSEENMA12034095

    For any two vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top comma we always have open vertical bar straight a with rightwards arrow on top. space straight b with rightwards arrow on top close vertical bar space less or equal than space open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar.

    Solution

    Assume that open vertical bar straight a with rightwards arrow on top close vertical bar space not equal to space 0 comma space space space open vertical bar straight b with rightwards arrow on top close vertical bar space not equal to space 0      open square brackets because space result space is space true space for space straight a with rightwards arrow on top space equals space 0 space or space straight b with rightwards arrow on top space equals space 0 close square brackets
    therefore space space space fraction numerator open vertical bar straight a with rightwards arrow on top. space straight b with rightwards arrow on top close vertical bar over denominator open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar end fraction space equals space fraction numerator open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar space cos space straight theta over denominator open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar end fraction where space straight theta space is space angle space between space vectors
therefore space space space space fraction numerator open vertical bar straight a with rightwards arrow on top. space straight b with rightwards arrow on top close vertical bar over denominator open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar end fraction space equals space cos space straight theta space less or equal than space 1
therefore space space space space space open vertical bar straight a with rightwards arrow on top. space straight b with rightwards arrow on top close vertical bar space less or equal than space space open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar

    Question 420
    CBSEENMA12034096

    For any two vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top, we always have open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar space less or equal than space open vertical bar straight a with rightwards arrow on top close vertical bar space plus space open vertical bar straight b with rightwards arrow on top close vertical bar

    Solution

    Assume that open vertical bar straight a with rightwards arrow on top close vertical bar space not equal to space 0 comma space space space open vertical bar straight b with rightwards arrow on top close vertical bar space not equal to space 0 space space space space space space space left square bracket because space space result space is space true space for space straight a with rightwards arrow on top space equals space 0 space or space straight b with rightwards arrow on top space equals space 0 right square bracket
                 open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar squared space equals space left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis squared space equals space straight a with rightwards arrow on top squared space plus space straight b with rightwards arrow on top squared space plus space 2 space straight a with rightwards arrow on top space straight b with rightwards arrow on top
                               equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared space plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space plus space 2 space open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar space cos space straight theta
less or equal than space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space plus space 2 space open vertical bar straight a with rightwards arrow on top close vertical bar space. space open vertical bar straight b with rightwards arrow on top close vertical bar space space space space space space space space space space space space space space space space space space space space space space left square bracket because space cos space straight theta space less or equal than space 1 right square bracket
space equals space left parenthesis open vertical bar straight a with rightwards arrow on top close vertical bar space plus space open vertical bar straight b with rightwards arrow on top close vertical bar right parenthesis squared
    therefore space space space space open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar squared space space less or equal than space open parentheses open vertical bar straight a with rightwards arrow on top close vertical bar space plus space open vertical bar straight b with rightwards arrow on top close vertical bar close parentheses squared
space space space space space space space space space open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar space less or equal than space open vertical bar straight a with rightwards arrow on top close vertical bar space plus space open vertical bar straight b with rightwards arrow on top close vertical bar

    Question 421
    CBSEENMA12034097

    If straight a with rightwards arrow on top is any vector, then show that
             straight a with rightwards arrow on top space equals space left parenthesis straight a with rightwards arrow on top space minus space straight i with hat on top right parenthesis space straight i with hat on top space plus space left parenthesis straight a with rightwards arrow on top. space straight j with hat on top right parenthesis space straight j with hat on top space plus space left parenthesis straight a with rightwards arrow on top space. space straight k with hat on top right parenthesis space straight k with hat on top.

    Solution
    straight a with hat on top space equals space straight a subscript 1 space straight i with hat on top space plus space straight a subscript 2 space straight j with hat on top space plus space straight a subscript 3 space straight k with hat on top                      ...(1)
          straight a with hat on top. space straight i with hat on top space equals straight a subscript 1 space straight i with hat on top. space straight i with hat on top space plus space straight a subscript 2 space straight j with hat on top space. space straight i with hat on top space plus space straight a subscript 3 space straight k with hat on top space. space straight i with hat on top space equals space straight a subscript 1 left parenthesis 1 right parenthesis space plus space straight a subscript 2 left parenthesis 0 right parenthesis space plus space straight a subscript 3 left parenthesis 0 right parenthesis
straight d with rightwards arrow on top space space straight i with hat on top space equals space straight a subscript 1
    Similarly,  straight a with rightwards arrow on top. space straight j with hat on top space equals straight a subscript 2 comma space straight a with rightwards arrow on top space. straight k with hat on top space equals space straight a subscript 3
       from (1), we get
                               straight a with rightwards arrow on top space equals space left parenthesis straight a with rightwards arrow on top. space straight i with hat on top right parenthesis space straight i with hat on top space plus space left parenthesis straight a with rightwards arrow on top. space straight j with hat on top right parenthesis space straight j with hat on top space plus space left parenthesis straight a with rightwards arrow on top. space straight k with hat on top right parenthesis space straight k with hat on top
    Question 422
    CBSEENMA12034098

    If straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top comma space 2 space straight i with hat on top plus 5 space straight j with hat on top comma space space 3 space straight i with hat on top space plus space 2 space straight j with hat on top space minus space 3 space straight k with hat on top space space and space straight i with hat on top space minus space 6 space straight j with hat on top space minus space straight k with hat on top, respectively, are the position vectors of points A, B, C and D, then find the angle between the straight lines AB and CD. Deduce that AB and CD are parallel.

    Solution

    Let straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top comma space straight d with rightwards arrow on top be position vectors of points A, B, C, D respectively.
    therefore space space space space straight a with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space 5 space straight j with hat on top comma space straight c with rightwards arrow on top space equals space 3 space straight i with hat on top space plus space 2 space straight j with hat on top space minus space 3 space straight k with hat on top comma space straight d with rightwards arrow on top space equals space straight i with hat on top space minus space 6 space straight j with hat on top space minus space straight k with hat on top
       AB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space space straight P. straight V. space of space straight A space equals space straight b with rightwards arrow on top minus straight a with rightwards arrow on top space equals space straight i with hat on top plus 4 space straight j with hat on top space minus space straight k with hat on top
CD with rightwards arrow on top space equals space straight P. straight V. space of space straight D space minus space straight P. straight V. space of space straight C space equals straight d with rightwards arrow on top space minus space straight c with rightwards arrow on top space equals space minus 2 space straight i with hat on top space minus space 8 space straight j with hat on top space plus space 2 space straight k with hat on top
    therefore space space space open vertical bar AB with rightwards arrow on top close vertical bar space equals space square root of 1 plus 16 plus 1 end root space equals space square root of 18 comma space space space open vertical bar CD with rightwards arrow on top close vertical bar space equals space square root of 4 plus 64 plus 4 end root space equals square root of 72
             AB with rightwards arrow on top space. space CD with rightwards arrow on top space equals space left parenthesis 1 right parenthesis thin space left parenthesis negative 2 right parenthesis space plus space left parenthesis 4 right parenthesis thin space left parenthesis negative 8 right parenthesis space plus space left parenthesis negative 1 right parenthesis thin space left parenthesis 2 right parenthesis space equals space minus 2 minus 32 minus 2 space equals space minus 36
    Let straight theta be angle between AB and CD
    therefore space space cos space straight theta space equals space fraction numerator AB with rightwards arrow on top. space CD with rightwards arrow on top over denominator open vertical bar AB with rightwards arrow on top close vertical bar space space open vertical bar CD with rightwards arrow on top close vertical bar end fraction space equals space fraction numerator negative 36 over denominator left parenthesis square root of 18 right parenthesis space left parenthesis square root of 72 right parenthesis end fraction space equals space fraction numerator negative 36 over denominator 3 square root of 2 space cross times space 6 space square root of 2 end fraction space equals negative 36 over 36 space equals space minus 1
therefore space space space straight theta space equals space straight pi space as space 0 space less or equal than space straight theta space less or equal than space straight pi
therefore space space AB space and space CD space are space parallel.

    Question 423
    CBSEENMA12034099

    Find the projection of the vector straight a with rightwards arrow on top space equals space 2 straight i with hat on top space plus space 3 straight j with hat on top space plus space 2 straight k with hat on top on the vector straight b with rightwards arrow on top space equals straight i with hat on top space plus space 2 space straight j with hat on top space plus space straight k with hat on top.

    Solution
    straight a with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space 3 space straight j with hat on top space plus space 2 space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top space plus space straight k with hat on top
    straight a space equals square root of 4 plus 9 plus 4 end root space equals square root of 17 comma space space space straight b space equals space square root of 1 plus 4 plus 1 end root space equals space square root of 6
    Projection of straight a with rightwards arrow on top space on space straight b with rightwards arrow on top space equals space fraction numerator straight a with rightwards arrow on top. space straight b with rightwards arrow on top over denominator straight b end fraction space equals space fraction numerator left parenthesis 2 right parenthesis thin space left parenthesis 1 right parenthesis space plus space left parenthesis 3 right parenthesis thin space left parenthesis 2 right parenthesis space plus space left parenthesis 2 right parenthesis thin space left parenthesis 1 right parenthesis over denominator square root of 6 end fraction
                                            equals space fraction numerator 2 plus 6 plus 2 over denominator square root of 6 end fraction space equals fraction numerator 10 over denominator square root of 6 end fraction space equals 5 over 3 square root of 6
    Question 424
    CBSEENMA12034100

    Find the projection of the vector straight i with hat on top space minus space straight j with hat on top on the vector straight i with hat on top space plus space straight j with hat on top.

    Solution

    Let straight a with rightwards arrow on top space equals straight i with hat on top space minus space straight j with hat on top comma space space space space straight b with rightwards arrow on top space equals straight i with hat on top space plus space straight j with hat on top
     therefore space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals left parenthesis 1 right parenthesis thin space left parenthesis 1 right parenthesis space plus space left parenthesis negative 1 right parenthesis thin space left parenthesis 1 right parenthesis space equals 1 minus 1 space equals space 0 comma space space straight b space equals space square root of 1 plus 1 end root space equals space square root of 2
    Projection of straight a with rightwards arrow on top space and space straight b with rightwards arrow on top space equals fraction numerator straight a with rightwards arrow on top. space straight b with rightwards arrow on top over denominator straight b end fraction equals space fraction numerator 0 over denominator square root of 2 end fraction space equals 0.

    Question 425
    CBSEENMA12034101
    Question 426
    CBSEENMA12034102

    Find the projection of 8 space straight i with hat on top space plus space straight j with hat on top in the direction of straight i with hat on top space plus space 2 space straight j with hat on top space minus space 2 space straight k with hat on top.

    Solution

    Let straight a with rightwards arrow on top space equals space 8 space straight i with hat on top space plus space straight j with hat on top comma space space space straight b with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top space minus space 2 space straight k with hat on top
    therefore space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space left parenthesis 8 right parenthesis thin space left parenthesis 1 right parenthesis space plus space left parenthesis 1 right parenthesis thin space left parenthesis 2 right parenthesis space plus space left parenthesis 0 right parenthesis thin space left parenthesis negative 2 right parenthesis space equals space 8 plus 2 minus 0 space equals space 10
space space space space space space space space space space space straight b space equals space square root of 1 plus 4 plus 4 end root space equals square root of 9 space equals space 3
    Required projection  = fraction numerator straight a with rightwards arrow on top. space straight b with rightwards arrow on top over denominator straight b end fraction space equals space 10 over 3

    Question 427
    CBSEENMA12034103

    Find the projection of straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top in the direction of straight i with hat on top space plus space straight j with hat on top.

    Solution

    Let straight a with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top
    therefore space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space left parenthesis 1 right parenthesis thin space left parenthesis 1 right parenthesis space plus space left parenthesis 1 right parenthesis thin space left parenthesis 1 right parenthesis space plus space left parenthesis 1 right parenthesis thin space left parenthesis 0 right parenthesis space equals space 1 plus 1 plus 0 space equals space 2
space space space space space space space space space space space space straight b space equals space square root of 1 plus 1 end root space equals space square root of 2
    Required projection equals space fraction numerator straight a with rightwards arrow on top. space straight b with rightwards arrow on top over denominator straight b end fraction space equals space fraction numerator 2 over denominator square root of 2 end fraction space equals square root of 2.

    Question 428
    CBSEENMA12034104

    Find the projection of straight b with rightwards arrow on top plus straight c with rightwards arrow on top on straight a with rightwards arrow on top where
             straight a with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top space plus space straight k with hat on top comma space space straight b with rightwards arrow on top space equals straight i with hat on top space plus space 3 space straight j with hat on top space plus space straight k with hat on top space and space straight c with rightwards arrow on top space equals space straight i with hat on top space plus space straight k with hat on top.

    Solution
    straight a with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top space plus space straight k with hat on top comma space space space space space straight b with rightwards arrow on top space equals space straight i with hat on top space plus space 3 space straight j with hat on top space plus space straight k with hat on top comma space space space space straight c with rightwards arrow on top space equals space straight i with hat on top space plus space straight k with hat on top
therefore space space space space space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top space equals space left parenthesis straight i with hat on top space plus space 3 space straight j with hat on top space plus space straight k with hat on top right parenthesis space plus space left parenthesis straight i with hat on top space plus space straight k with hat on top right parenthesis space equals space 2 space straight i with hat on top space plus space 3 space straight j with hat on top space plus space space 2 space straight k with hat on top
    Projection of left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space on space straight a with rightwards arrow on top
                             equals space fraction numerator left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space. space straight a with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top close vertical bar end fraction
equals space fraction numerator left parenthesis 2 straight i with hat on top space plus space 3 straight j with hat on top space plus space 2 space straight k with hat on top right parenthesis. space space left parenthesis straight i with hat on top space plus space 2 space straight j with hat on top space plus space straight k with hat on top right parenthesis over denominator square root of left parenthesis 1 right parenthesis squared plus left parenthesis 2 right parenthesis space plus space left parenthesis 1 right parenthesis squared end root end fraction
equals space fraction numerator left parenthesis 2 right parenthesis thin space left parenthesis 1 right parenthesis space plus space left parenthesis 3 right parenthesis thin space left parenthesis 2 right parenthesis space plus space left parenthesis 2 right parenthesis thin space left parenthesis 1 right parenthesis over denominator square root of 1 plus 4 plus 1 end root end fraction space equals fraction numerator 2 plus 6 plus 2 over denominator square root of 6 end fraction space equals fraction numerator 10 over denominator square root of 6 end fraction
    Question 429
    CBSEENMA12034105

    Find λ when the scalar projection of straight a with rightwards arrow on top space equals space straight lambda straight i with hat on top space plus space straight j with hat on top space plus space 4 straight k with hat on top space space and space straight b with rightwards arrow on top space equals space 2 straight i with hat on top space plus space 6 straight j with hat on top space plus space 3 straight k with hat on top space is space 4 space units.

    Solution

    Here   straight a with rightwards arrow on top space equals space straight lambda space straight i with hat on top space plus space straight j with hat on top space plus space 4 space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space 6 space straight j with hat on top space plus space 3 space straight k with hat on top
    therefore space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space square root of 4 plus 36 plus 9 end root equals space square root of 49 space equals space 7
                    straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space left parenthesis straight lambda right parenthesis space left parenthesis 2 right parenthesis space plus space left parenthesis 1 right parenthesis thin space left parenthesis 6 right parenthesis space plus space left parenthesis 4 right parenthesis thin space left parenthesis 3 right parenthesis space equals space 2 space straight lambda space plus 6 plus 12 space equals space 2 straight lambda plus 18
    Scalar projection of straight a with rightwards arrow on top space and space straight b with rightwards arrow on top = fraction numerator straight a with rightwards arrow on top. space straight b with rightwards arrow on top over denominator open vertical bar straight b with rightwards arrow on top close vertical bar end fraction
     therefore space space space 4 space equals space fraction numerator 2 space straight lambda space plus space 18 over denominator 7 end fraction space space space space space rightwards double arrow space space space space 28 space equals space 2 straight lambda plus 18 space space space space rightwards double arrow space space space 2 space straight lambda space equals space 10
therefore space space space space space straight lambda space equals space 5

    Question 430
    CBSEENMA12034106

    Find the angle between the vectors straight a with rightwards arrow on top space equals straight i with hat on top space minus space straight j with hat on top space plus space straight k with hat on top space and straight b with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space minus space straight k with hat on top.

    Solution
    Let straight theta be angle between the vectors
                        straight a with rightwards arrow on top space equals space straight i with hat on top space minus space straight j with hat on top space plus space straight k with hat on top space and space straight b with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space minus space straight k with hat on top
    Now,      straight a space equals square root of left parenthesis 1 right parenthesis squared plus left parenthesis negative 1 right parenthesis squared plus left parenthesis 1 right parenthesis squared end root space equals space square root of 1 plus 1 plus 1 end root space equals square root of 3
                  straight b equals space square root of left parenthesis 1 right parenthesis squared plus left parenthesis 1 right parenthesis squared plus left parenthesis negative 1 right parenthesis squared end root space equals square root of 1 plus 1 plus 1 end root space equals square root of 3
              straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space left parenthesis 1 right parenthesis thin space left parenthesis 1 right parenthesis space plus space left parenthesis negative 1 right parenthesis thin space left parenthesis 1 right parenthesis space plus space left parenthesis 1 right parenthesis thin space left parenthesis negative 1 right parenthesis space equals space 1 minus 1 minus 1 space equals negative 1
    Now    straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space straight a space straight b space cos space straight theta space space space rightwards double arrow space space space space minus 1 space equals space left parenthesis square root of 3 right parenthesis thin space left parenthesis square root of 3 right parenthesis space cos space straight theta
    therefore space space space space space 3 space cos space straight theta space equals space minus 1 space space space space space space space space space or space space space cos space straight theta space equals space minus 1 third
therefore space space space space space space space space space straight theta space equals space cos to the power of negative 1 end exponent space open parentheses negative 1 third close parentheses.
    Question 432
    CBSEENMA12034108
    Question 433
    CBSEENMA12034109

    Find the cosine of the angle between the vectors
    straight a with rightwards arrow on top space equals space 5 space straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top space and space straight b with rightwards arrow on top space equals space minus 2 space straight i with hat on top space plus space straight j with hat on top space plus space 3 space straight k with hat on top

    Solution

    Here,   straight a with rightwards arrow on top space equals space 5 straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals negative 2 space straight i with hat on top space plus space straight j with hat on top space plus space 3 space straight k with hat on top
    therefore space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space left parenthesis 5 straight i with hat on top plus straight j with hat on top plus straight k with hat on top right parenthesis. space left parenthesis negative 2 straight i with hat on top space plus straight j with hat on top plus 3 space straight k with hat on top right parenthesis
space space space space space space space space space space space space space space space space space equals space left parenthesis 5 right parenthesis thin space left parenthesis negative 2 right parenthesis space plus space left parenthesis 1 right parenthesis thin space left parenthesis 1 right parenthesis space plus space left parenthesis 1 right parenthesis thin space left parenthesis 3 right parenthesis space equals negative 10 plus 1 plus 3 space equals space minus 6
    Let straight theta be angle between straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.
    therefore space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space straight a space straight b space cos space straight theta
       rightwards double arrow space space space minus 6 space equals space square root of 5 plus 1 plus 1 end root space square root of 4 plus 1 plus 9 end root space cos space straight theta
rightwards double arrow space space minus 6 space equals space square root of 7 space square root of 14 space cos space straight theta space space rightwards double arrow space space space space minus 6 space equals space 7 square root of 2 space cos space straight theta
therefore space space space cos space straight theta space equals space minus fraction numerator 6 over denominator 7 square root of 2 end fraction

    Question 434
    CBSEENMA12034110

    If straight a with rightwards arrow on top makes equal angles with straight i with hat on top comma space straight j with hat on top space and space straight k with hat on top and has magnitude 3, then prove that the angle between straight a with rightwards arrow on top and each of straight i with hat on top comma space straight j with hat on top space and space straight k with hat on top is cos to the power of negative 1 end exponent open parentheses fraction numerator 1 over denominator square root of 3 end fraction close parentheses.

    Solution

    Let straight a with rightwards arrow on top space equals straight a subscript 1 straight i with hat on top space plus space straight a subscript 2 straight j with hat on top space plus space straight a subscript 3 straight k with hat on top such that open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 3 and O be the angle which straight a with rightwards arrow on top makes with straight i with hat on top comma space straight j with hat on top comma space straight k with hat on top.
    therefore space space space space cos space straight theta space equals space fraction numerator straight a with rightwards arrow on top. space straight i with hat on top over denominator open vertical bar straight a with rightwards arrow on top close vertical bar. space open vertical bar straight i with hat on top close vertical bar end fraction space equals space fraction numerator straight a subscript 1 over denominator left parenthesis 3 right parenthesis left parenthesis 1 right parenthesis end fraction space space space rightwards double arrow space space space space straight a subscript 1 space equals space 3 space cos space straight theta
    Again cos space straight theta space equals space fraction numerator straight a with rightwards arrow on top. space straight j with hat on top over denominator open vertical bar straight a with rightwards arrow on top close vertical bar. space open vertical bar straight j with hat on top close vertical bar end fraction space equals space fraction numerator straight a subscript 2 over denominator left parenthesis 3 right parenthesis thin space left parenthesis 1 right parenthesis end fraction space space space rightwards double arrow space space straight a subscript 2 space equals space 3 space cos space straight theta
    and cos space straight theta space equals space fraction numerator straight a with rightwards arrow on top. space straight k with hat on top over denominator open vertical bar straight a with rightwards arrow on top close vertical bar. space open vertical bar straight j with hat on top close vertical bar end fraction space equals space fraction numerator straight a subscript 3 over denominator left parenthesis 3 right parenthesis thin space left parenthesis 1 right parenthesis space end fraction space space rightwards double arrow space space straight a subscript 3 space equals space 3 space cos space straight theta
    Also, open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 3                rightwards double arrow space space space space space square root of straight a subscript 1 squared plus straight a subscript 2 squared plus straight a subscript 3 squared end root space equals space 3
    rightwards double arrow space space space square root of 9 space cos squared straight theta space plus space 9 space cos squared straight theta space plus space 9 space cos squared space straight theta end root space equals space 3 space space space space space space space rightwards double arrow space space space square root of 27 space cos squared straight theta end root space equals space 3
rightwards double arrow space space space 3 square root of 3 space cos space straight theta space equals space 3 space space space space space space rightwards double arrow space space space cos space straight theta space equals space fraction numerator 1 over denominator square root of 3 end fraction
therefore space space space space space space space straight theta space space equals space cos to the power of negative 1 end exponent space open parentheses fraction numerator 1 over denominator square root of 3 end fraction close parentheses

    Question 435
    CBSEENMA12034111

    Express the vector straight a with rightwards arrow on top space equals space 5 space straight i with hat on top space minus space 2 space straight j with hat on top space plus space 5 space straight k with hat on top as sum of two vectors such that one is parallel to the vector straight b with rightwards arrow on top space equals space 3 space straight i with hat on top space plus space straight k with hat on top and other is perpendicular to straight b with rightwards arrow on top.

    Solution

                           straight a with rightwards arrow on top space equals space 5 straight i with hat on top space minus space 2 straight j with hat on top plus 5 straight k with hat on top comma space space space straight b with rightwards arrow on top space equals 3 straight i with hat on top space plus straight k with hat on top
    Let straight a with rightwards arrow on top space equals space straight A with rightwards arrow on top space plus space straight B with rightwards arrow on top space where space straight A with rightwards arrow on top space is space parallel space to space straight b with rightwards arrow on top space and space straight B with rightwards arrow on top space is space perpendicular space to space straight b with rightwards arrow on top.
    therefore space space space space straight A with rightwards arrow on top space equals space straight lambda left parenthesis 3 space straight i with hat on top space plus space straight k with hat on top right parenthesis space equals space 3 space straight lambda space straight i with hat on top space plus space straight lambda space straight k with hat on top
    and straight B with rightwards arrow on top space equals space straight a with rightwards arrow on top space minus space straight A with rightwards arrow on top space equals space left parenthesis 5 straight i with hat on top plus straight j with hat on top space plus space 5 space straight k with hat on top right parenthesis space minus space left parenthesis 3 space straight lambda space straight i with hat on top space plus space straight lambda space straight k with hat on top right parenthesis
                equals space left parenthesis 5 space minus 3 space straight lambda right parenthesis space straight i with hat on top space plus space straight j with hat on top space plus space left parenthesis 5 minus straight lambda right parenthesis space straight k with hat on top
    Since straight B with rightwards arrow on top is perpendicular to straight b with rightwards arrow on top
    therefore space space space space straight B with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0
rightwards double arrow space space space left parenthesis 5 space minus space 3 space straight lambda right parenthesis space left parenthesis 3 right parenthesis space plus space left parenthesis 1 right parenthesis thin space left parenthesis 0 right parenthesis space plus space left parenthesis 5 minus straight lambda right parenthesis space left parenthesis 1 right parenthesis space equals space 0
rightwards double arrow space space space space 15 minus 9 straight lambda plus 5 minus straight lambda space equals space 0 space space space space space space space space space space space space space space space rightwards double arrow space space 10 straight lambda space equals space 20 space space space space rightwards double arrow space space space straight lambda space equals space 2
therefore space space space space space space straight A with rightwards arrow on top space equals space 6 straight i with hat on top space plus space 2 straight k with hat on top comma space space space straight B with rightwards arrow on top space equals space minus straight i with hat on top plus space straight j with hat on top space plus space 3 straight k with hat on top


    Question 436
    CBSEENMA12034112

    Decompose the vector 6 straight i with hat on top space minus space 3 straight j with hat on top space minus space 6 straight k with hat on top into vectors which are parallel and perpendicular to the vector straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top.

    Solution

    Let straight a with rightwards arrow on top space equals space 6 straight i with hat on top space minus space 3 straight j with hat on top minus space 6 straight k with hat on top be decomposed into two vectors straight A with rightwards arrow on top space and space straight B with rightwards arrow on top.
    where straight A with rightwards arrow on top is parallel to straight b with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top space and space straight B with rightwards arrow on top space is space perpendicular space to space straight b with rightwards arrow on top.
    therefore space space space straight A with rightwards arrow on top space equals space straight lambda space left parenthesis straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top right parenthesis space equals space straight lambda space straight i with hat on top space plus space straight lambda space straight j with hat on top space plus space straight lambda space straight k with hat on top
    and     straight a with rightwards arrow on top space equals space straight A with rightwards arrow on top space plus space straight B with rightwards arrow on top space space space space space space space space space space space space space space space space space rightwards double arrow space space space space straight B with rightwards arrow on top space equals space straight a with rightwards arrow on top space minus space straight A with rightwards arrow on top
    therefore space space space straight B with rightwards arrow on top space equals space left parenthesis 6 minus space straight lambda right parenthesis space straight i with hat on top space minus space left parenthesis straight lambda plus 3 right parenthesis space straight j with hat on top space minus space left parenthesis straight lambda minus 6 right parenthesis space straight k with hat on top
    because space space straight B with rightwards arrow on top space is space perpendicular space to space straight b with rightwards arrow on top.
therefore space space space space straight b with rightwards arrow on top. space straight B with rightwards arrow on top space equals space 0
rightwards double arrow space space left parenthesis 6 minus straight lambda right parenthesis space left parenthesis 1 right parenthesis space minus space left parenthesis straight lambda plus 3 right parenthesis space left parenthesis 1 right parenthesis space minus space left parenthesis straight lambda plus 6 right parenthesis space left parenthesis 1 right parenthesis space equals space 0
therefore space space space space 6 space minus space straight lambda space minus straight lambda minus 3 minus straight lambda minus 6 space equals space 0 space space space space space space space rightwards double arrow space space space space space 3 space straight lambda space equals space minus 3 space space space space rightwards double arrow space space space straight lambda space equals space minus 1
therefore space space space required space vectors space are
space space space space space space space space space space space space space minus straight i with hat on top space minus space straight j with hat on top space minus space straight k with hat on top comma space space space space space 7 straight i with hat on top space minus space 2 space straight j with hat on top space minus space 5 space straight k with hat on top

    Question 437
    CBSEENMA12034113

    Express 2 straight i with hat on top space minus straight j with hat on top space plus space 3 straight k with hat on top as the sum of a vector parallel, and a vector parallel, and a vector perpendicular to 2 straight i with hat on top plus 4 straight j with hat on top minus 2 straight k with hat on top.

    Solution

    Let straight a with rightwards arrow on top space equals space 2 straight i with hat on top space minus space straight j with hat on top plus 3 straight k with hat on top be expressed as
                straight a with rightwards arrow on top space equals space straight A with rightwards arrow on top space plus straight B with rightwards arrow on top
    where straight A with rightwards arrow on top is parallel to straight b with rightwards arrow on top space equals 2 straight i with hat on top plus 4 straight j with hat on top minus 2 straight k with hat on top and B is perpendicular to straight b with rightwards arrow on top.
    therefore space space space straight A with rightwards arrow on top space equals space straight lambda left parenthesis 2 straight i with hat on top plus 4 straight j with hat on top minus 2 straight k with hat on top right parenthesis space equals space 2 straight lambda straight i with hat on top space plus space 4 straight lambda straight j with hat on top space minus 2 straight lambda straight k with hat on top
and space straight B with rightwards arrow on top space equals space straight a with rightwards arrow on top minus straight A with rightwards arrow on top space equals left parenthesis 2 minus 2 straight lambda right parenthesis straight i with hat on top space minus space left parenthesis 1 plus 4 straight lambda right parenthesis straight j with hat on top space plus space left parenthesis 3 plus 2 straight lambda right parenthesis straight k with hat on top
therefore space straight B with rightwards arrow on top space is space perpendicular space to space straight b with rightwards arrow on top
because space space straight B with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0
therefore space space space space left parenthesis 2 minus 2 straight lambda right parenthesis space left parenthesis 2 right parenthesis space minus space left parenthesis 1 plus 4 straight lambda right parenthesis space left parenthesis 4 right parenthesis space plus space left parenthesis 3 plus 2 straight lambda right parenthesis space left parenthesis negative 2 right parenthesis space equals space 0
therefore space space space space 4 minus 4 straight lambda minus 4 minus 16 straight lambda minus 6 minus 4 straight lambda space equals 0
rightwards double arrow space space space 24 straight lambda space equals space minus 6 space space space space space space space space space space space space space space space rightwards double arrow space straight lambda space equals space minus 1 fourth
therefore space space space required space vectors space are
space space space space space space space space minus 1 half straight i with hat on top space minus space straight j with hat on top space plus space 1 half straight k with hat on top space and space 5 over 2 straight i with hat on top space plus space 5 over 2 straight k with hat on top
space space therefore space space space 2 space straight i with hat on top space minus space straight j with hat on top space plus space 3 space straight k with hat on top space equals space open parentheses negative 1 half straight i with hat on top space minus space straight j with hat on top space plus space 1 half straight k with hat on top close parentheses space plus space open parentheses 5 over 2 straight i with hat on top space plus space 5 over 2 straight k with hat on top close parentheses

    Question 438
    CBSEENMA12034114

    Show that the vectors straight a with rightwards arrow on top space equals space straight i with hat on top space minus space 3 space straight j with hat on top space minus space 5 space straight k with hat on top comma space straight b with rightwards arrow on top space equals 2 space straight i with hat on top space minus straight j with hat on top plus straight k with hat on top comma space and space straight c with rightwards arrow on top space equals straight i with hat on top plus 2 space straight j with hat on top plus 6 space straight k with hat on top form a right angled triangle. 

    Solution

    Here,    
            straight a with rightwards arrow on top space equals space straight i with hat on top space minus space 3 space straight j with hat on top space minus space 5 space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals 2 space straight i with hat on top space minus space straight j with hat on top space plus space straight k with hat on top comma space straight c with rightwards arrow on top space equals straight i with hat on top space plus space 2 space straight j with hat on top space plus space 6 space straight k with hat on top
    Now, straight c with rightwards arrow on top plus straight a with rightwards arrow on top space equals space left parenthesis straight i with hat on top space plus space 2 straight j with hat on top space plus space 6 straight k with hat on top right parenthesis space plus space left parenthesis straight i with hat on top space minus space 3 space straight j with hat on top space minus space 5 space straight k with hat on top right parenthesis space equals 2 straight i with hat on top space minus space straight j with hat on top space plus space straight k with hat on top space equals space straight b with rightwards arrow on top
    therefore space space space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top space are space coplanar space vectors space and space form space the space sides space of space straight a space triangle.
                straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space left parenthesis 1 right parenthesis thin space left parenthesis 2 right parenthesis space plus space left parenthesis negative 3 right parenthesis thin space left parenthesis negative 1 right parenthesis space plus space left parenthesis negative 5 right parenthesis thin space left parenthesis 1 right parenthesis space equals space 2 plus 3 space minus space 5 space equals 0
    therefore space space straight a with rightwards arrow on top space and space straight b with rightwards arrow on top space are space perpendicular.
therefore space space space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top space form space straight a space right space angled space triangle.

    Question 439
    CBSEENMA12034115

    Show that the vectors 2 straight i with hat on top minus straight j with hat on top plus straight k with hat on top comma space straight b with rightwards arrow on top space equals space straight i with hat on top space minus space 3 straight j with hat on top space minus space 5 straight k with hat on top comma space straight c with rightwards arrow on top space equals space 3 straight i with hat on top minus 4 straight j with hat on top minus 4 straight k with hat on top form the vertices of a right angled triangle. 

    Solution

    Let 
    straight a with rightwards arrow on top space equals 2 straight i with hat on top space minus space straight j with hat on top space plus space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals straight i with hat on top minus 3 space straight j with hat on top space minus space 5 space straight k with hat on top comma space space space straight c with rightwards arrow on top space equals space 3 space straight i with hat on top space minus space 4 space straight j with hat on top space minus space 4 space straight k with hat on top
    be the position vectors of A. B, C respectively.
    therefore space space space space AB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A space equals straight b with rightwards arrow on top minus straight a with rightwards arrow on top
                                  equals left parenthesis straight i with hat on top space space minus space 3 space straight j with hat on top space minus space space 5 straight k with hat on top right parenthesis space minus space left parenthesis 2 straight i with hat on top minus straight j with hat on top plus straight k with hat on top right parenthesis space equals space minus straight i with hat on top minus 2 space straight j with hat on top space minus space 6 space straight k with hat on top
             BC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight B space equals space straight c with rightwards arrow on top minus straight b with rightwards arrow on top
space space space space space space space equals space left parenthesis 3 space straight i with hat on top space minus space 4 space straight j with hat on top space minus space space 4 space straight k with hat on top right parenthesis space minus space left parenthesis straight i with hat on top space minus space 3 space straight j with hat on top space minus space 5 space straight k with hat on top right parenthesis space equals space 2 straight i with hat on top space minus space straight j with hat on top space plus space straight k with hat on top
CA with rightwards arrow on top space equals space straight P. straight V. space of space straight A space minus space straight P. straight V. space of space straight C space equals space straight a with rightwards arrow on top minus straight c with rightwards arrow on top
space space space space space space space equals space left parenthesis 2 space straight i with hat on top space minus space straight j with hat on top space plus space straight k with hat on top right parenthesis space minus space left parenthesis 3 space straight i with hat on top space minus space 4 space straight j with hat on top space minus space 4 space straight k with hat on top right parenthesis space equals space minus straight i with hat on top space plus space 3 space straight j with hat on top space plus space 5 space straight k with hat on top
therefore space space space AB with rightwards arrow on top plus BC with rightwards arrow on top space equals straight i with hat on top space space minus space 3 space straight j with hat on top space minus space 5 space straight k with hat on top space equals space minus CA with rightwards arrow on top
therefore space space space AB with rightwards arrow on top plus BC with rightwards arrow on top plus CA with rightwards arrow on top space equals space 0 with rightwards arrow on top
Again comma space space BC with rightwards arrow on top. space CA with rightwards arrow on top space equals space left parenthesis 2 right parenthesis thin space left parenthesis negative 1 right parenthesis space plus space left parenthesis negative 1 right parenthesis thin space left parenthesis 3 right parenthesis space plus space left parenthesis 1 right parenthesis thin space left parenthesis 5 right parenthesis space equals negative 2 minus 3 plus 5 space equals space 0
therefore space space space space BC with rightwards arrow on top space and space CA with rightwards arrow on top space are space perpendicular
therefore space space space increment ABC space is space right space angled
    therefore given position vectors straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top form the vertices of a right angled triangle.

    Question 440
    CBSEENMA12034116
    Question 441
    CBSEENMA12034117

    Show that the points whose position vectors are 
    straight a with rightwards arrow on top space equals space 4 space straight i with hat on top space minus space 3 space straight j with hat on top space plus space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space 4 space straight j with hat on top space plus space space 5 space straight k with hat on top comma space space straight c with rightwards arrow on top space equals straight i with hat on top space minus space straight j with hat on top form a right angled triangle.

    Solution

    Let straight a with rightwards arrow on top space equals space 4 space straight i with hat on top space minus space 3 space straight j with hat on top space plus space straight k with hat on top comma space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space 4 space straight j with hat on top space plus space 5 space straight k with hat on top comma space space straight c with rightwards arrow on top space equals straight i with hat on top space minus space straight j with hat on top be the position vectors of A, B, C respectively.
    therefore space space AB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A space equals space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space 4 space straight j with hat on top space plus space 5 space straight k with hat on top space minus space 4 space straight i with hat on top space plus space 3 space straight j with hat on top space minus space straight k with hat on top
space space space space space space space space space space space space space equals space minus 2 space straight i with hat on top space minus space straight j with hat on top space plus space 4 space straight k with hat on top
        BC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight B space equals space straight c with rightwards arrow on top minus straight b with rightwards arrow on top space equals straight i with hat on top minus straight j with hat on top space minus space 2 space straight i with hat on top space plus space 4 space straight j with hat on top space minus space 5 space straight k with hat on top
space space space space space space equals space minus straight i with hat on top space plus space 3 space straight j with hat on top space minus space 5 space straight k with hat on top
       CA with rightwards arrow on top space equals space straight P. straight V. space of space straight A space minus space straight P. straight V. space of space straight C space equals space straight a with rightwards arrow on top minus straight c with rightwards arrow on top space equals 4 space straight i with hat on top space minus space 3 space straight j with hat on top space plus space straight k with hat on top space minus space straight i with hat on top space plus space straight j with hat on top
space space space space space equals space 3 straight i with hat on top space minus space 2 straight j with hat on top space plus space straight k with hat on top
therefore space space AB with rightwards arrow on top space plus space BC with rightwards arrow on top space equals space minus 3 space straight i with hat on top space space plus space 2 space straight j with hat on top space minus space straight k with hat on top space equals space minus CA with rightwards arrow on top
therefore space space AB with rightwards arrow on top comma space stack BC comma with rightwards arrow on top space CA with rightwards arrow on top space are space co minus planar space and space form space the space sides space of space straight a space triangle. space
Again comma space AB with rightwards arrow on top. space CA with rightwards arrow on top space equals left parenthesis negative 2 right parenthesis thin space left parenthesis 3 right parenthesis space plus space left parenthesis negative 1 right parenthesis thin space left parenthesis negative 2 right parenthesis space plus space left parenthesis 4 right parenthesis thin space left parenthesis 1 right parenthesis space equals space minus 6 plus 2 plus 4 space equals space 0
therefore space space space space AB with rightwards arrow on top space and space CA with rightwards arrow on top space are space perpendicular space space rightwards double arrow space space increment ABC space is space right space angled.

    Question 443
    CBSEENMA12034119

    Show that 1 over 7 left parenthesis 2 straight i with hat on top space plus space 3 straight j with hat on top space plus space 6 straight k with hat on top right parenthesis comma space space 1 over 7 left parenthesis 3 straight i with hat on top minus 6 straight j with hat on top plus 2 straight k with hat on top right parenthesis comma space space 1 over 7 left parenthesis 6 straight i with hat on top plus 2 straight j with hat on top minus 3 straight k with hat on top right parenthesis are mutually perpendicular unit vectors.

    Solution

    Let straight a with rightwards arrow on top space equals space 1 over 7 left parenthesis 2 straight i with hat on top space plus space 3 straight j with hat on top space plus space 6 straight k with hat on top right parenthesis space equals space 2 over 7 straight i with hat on top space plus space 3 over 7 straight j with hat on top space plus space 6 over 7 straight k with hat on top      
    straight b with rightwards arrow on top space equals space 1 over 7 left parenthesis 3 straight i with hat on top minus space 6 straight j with hat on top space plus space 2 straight k with hat on top right parenthesis space equals 3 over 7 straight i with hat on top space minus space 6 over 7 straight j with hat on top space plus space 2 over 7 straight k with hat on top
straight c with rightwards arrow on top space equals space 1 over 7 left parenthesis 6 straight i with hat on top plus space 2 straight j with hat on top space minus space 3 straight k with hat on top right parenthesis space equals space 6 over 7 straight i with hat on top plus 2 over 7 straight j with hat on top minus 3 over 7 straight k with hat on top
    therefore space straight a space equals space square root of open parentheses 2 over 7 close parentheses squared plus space open parentheses 3 over 7 close parentheses squared plus open parentheses 6 over 7 close parentheses squared end root space equals space square root of 4 over 49 plus 9 over 49 plus 36 over 49 end root space equals space square root of 49 over 49 end root space equals space 1
         straight b space equals space square root of open parentheses 3 over 7 close parentheses squared plus open parentheses fraction numerator negative 6 over denominator 7 end fraction close parentheses squared plus open parentheses 2 over 7 close parentheses squared end root space equals space square root of 9 over 49 plus 36 over 49 plus 4 over 49 end root space equals square root of 49 over 49 end root space equals space 1
straight c space equals space square root of open parentheses 6 over 7 close parentheses squared plus open parentheses 2 over 7 close parentheses squared plus open parentheses fraction numerator negative 3 over denominator 7 end fraction close parentheses squared end root space equals square root of 36 over 49 plus 4 over 49 plus 9 over 49 end root space equals space square root of 49 over 49 end root space equals space 1
    therefore space space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top space are space unit space vectors.
    straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space open parentheses 2 over 7 close parentheses space open parentheses 3 over 7 close parentheses space plus space open parentheses 3 over 7 close parentheses space open parentheses fraction numerator negative 6 over denominator 7 end fraction close parentheses space plus space open parentheses 6 over 7 close parentheses space open parentheses 2 over 7 close parentheses space equals space 6 over 49 minus 18 over 49 plus 12 over 49 space equals space 0
straight a with rightwards arrow on top. space straight c with rightwards arrow on top space equals space open parentheses 2 over 7 close parentheses space open parentheses 6 over 7 close parentheses plus open parentheses 3 over 7 close parentheses open parentheses 2 over 7 close parentheses plus open parentheses 6 over 7 close parentheses space open parentheses fraction numerator negative 3 over denominator 7 end fraction close parentheses space equals space 12 over 49 plus 6 over 49 minus 18 over 49 space equals 0
straight b with rightwards arrow on top. straight c with rightwards arrow on top space equals space open parentheses 3 over 7 close parentheses space open parentheses 6 over 7 close parentheses plus open parentheses fraction numerator negative 6 over denominator 7 end fraction close parentheses space open parentheses 2 over 7 close parentheses plus open parentheses 2 over 7 close parentheses space open parentheses fraction numerator negative 3 over denominator 7 end fraction close parentheses space space equals 18 over 49 minus 12 over 49 minus 6 over 49 equals 0
    therefore space space space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top space are space mutually space orthogonal space vectors.

    Question 445
    CBSEENMA12034121

    If a unit vector straight a with rightwards arrow on top makes angle straight pi over 4 space with space straight i with hat on top comma space space straight pi over 3 space with space straight j with hat on top and an acute angle straight theta with straight k with hat on top, then find the component of straight a with rightwards arrow on top and the angle straight theta.

    Solution
    Let a1 , a, a3 be scalar components of straight a with rightwards arrow on top.
       space therefore space space space space straight a with rightwards arrow on top space equals space straight a subscript 1 space straight i with hat on top space plus space straight a subscript 2 space straight j with hat on top space plus space straight a subscript 3 space straight k with hat on top
     Since straight a with rightwards arrow on top makes an angle straight pi over 4 space with space straight i with hat on top
    therefore space space cos space straight pi over 4 space equals space fraction numerator straight a with rightwards arrow on top. space straight i with hat on top over denominator open vertical bar straight a with rightwards arrow on top close vertical bar. space open vertical bar straight i with hat on top close vertical bar end fraction space space space space space rightwards double arrow space space space space fraction numerator 1 over denominator square root of 2 end fraction space equals space fraction numerator straight a subscript 1 over denominator left parenthesis 1 right parenthesis thin space left parenthesis 1 right parenthesis end fraction space space space space space space space space space space space space space open square brackets because space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 1 close square brackets
rightwards double arrow space space space straight a subscript 1 space equals space fraction numerator 1 over denominator square root of 2 end fraction
    Again, straight a with rightwards arrow on top makes an angle straight pi over 3 space with space straight j with hat on top
    therefore space space cos space straight pi over 3 space equals space fraction numerator straight a with rightwards arrow on top. space straight i with hat on top over denominator open vertical bar straight a with rightwards arrow on top close vertical bar. space open vertical bar straight j with hat on top close vertical bar end fraction space space space space space rightwards double arrow space space space space 1 half space equals space fraction numerator straight a subscript 2 over denominator left parenthesis 1 right parenthesis thin space left parenthesis 1 right parenthesis space end fraction space space space space space rightwards double arrow space space space straight a subscript 2 space equals space 1 half
    Since straight a with rightwards arrow on top is a unit vector
    therefore space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 1 space space space space space space space space space space space space space space space space space space space rightwards double arrow space space space space open vertical bar straight a with rightwards arrow on top close vertical bar squared space equals space 1 space space space space space rightwards double arrow space space space straight a subscript 1 squared plus straight a subscript 2 squared plus straight a subscript 3 squared space equals space 1
therefore space space space 1 half plus 1 fourth plus straight a subscript 3 squared space equals space 1 space space space space space space rightwards double arrow space space space straight a subscript 3 squared space equals 1 fourth space space space space rightwards double arrow space straight a subscript 3 space equals space plus-or-minus 1 half
Since space straight theta space space is space angle space between space straight a with rightwards arrow on top space and space straight k with hat on top
therefore space space cos space straight theta space equals space fraction numerator straight a with rightwards arrow on top. space straight k with hat on top over denominator open vertical bar straight a with rightwards arrow on top close vertical bar. space open vertical bar straight k with hat on top close vertical bar end fraction space equals fraction numerator straight a subscript 3 over denominator left parenthesis 1 right parenthesis left parenthesis 1 right parenthesis end fraction space equals space plus-or-minus 1 half.

    ∴    = 60°, 120°
    Rejecting straight theta = 120° as ө is given to be acute,
    we have straight theta = 160°
    Now scalar components of straight a with rightwards arrow on top are fraction numerator 1 over denominator square root of 2 end fraction comma space 1 half comma space plus-or-minus 1 half and vector component of straight a with rightwards arrow on top are fraction numerator 1 over denominator square root of 2 end fraction space straight i with hat on top comma space 1 half space straight j with hat on top space plus-or-minus 1 half straight k with hat on top.
    Also   straight theta space equals space 60 degree.

    Question 446
    CBSEENMA12034122

    If A, B, C have position vectors (0, 1, 1) (3, 1, 5), (0. 3, 3) respectively, then show that the ∆ABC is right angled at C.

    Solution

    Let straight a with rightwards arrow on top space equals space left parenthesis 0 comma space 1 comma space 1 right parenthesis space equals space straight j with hat on top space plus space straight k with hat on top comma space space space space space space straight b with rightwards arrow on top space equals space left parenthesis 3 comma space 1 comma space 5 right parenthesis space equals space 3 space straight i with hat on top space plus space straight j with hat on top space plus space 5 space straight k with hat on top comma
          straight i with hat on top space equals space left parenthesis 0 comma space 3 comma space 3 right parenthesis space equals space 3 straight j with hat on top plus 3 straight k with hat on top be the position vectors of A, B, C respectively.
        CA with rightwards arrow on top space equals space straight P. straight V. space of space straight A space minus space straight P. straight V. space of space straight C space equals space straight a with rightwards arrow on top space minus space straight c with rightwards arrow on top space equals space minus 2 space straight j with hat on top space minus space 2 space straight k with hat on top
CB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight C space equals space straight b with rightwards arrow on top minus straight c with rightwards arrow on top space equals space 3 space straight i with hat on top space minus space 2 space straight j with hat on top space plus space 2 space straight k with hat on top
CA with rightwards arrow on top. space CB with rightwards arrow on top space equals space left parenthesis negative 2 straight j with hat on top space minus space 2 straight k with hat on top right parenthesis. space left parenthesis 3 straight i with hat on top space minus space 2 straight j with hat on top plus 2 straight k with hat on top right parenthesis
space space space space space space space space space space space space space space space space equals space left parenthesis 0 right parenthesis thin space left parenthesis 3 right parenthesis space plus space left parenthesis negative 2 right parenthesis space left parenthesis negative 2 right parenthesis plus space left parenthesis negative 2 right parenthesis thin space left parenthesis 2 right parenthesis space equals space 0 plus 4 minus 4 space equals space 0
therefore space space space CA with rightwards arrow on top space and space CB with rightwards arrow on top space are space perpendicular
therefore space space space space increment ABC space is space right space angled space at space straight C.

    Question 447
    CBSEENMA12034123

    If a unit vector straight a with rightwards arrow on top makes angles straight pi over 3 with straight i with hat on top comma  straight pi over 4 space with space straight j with hat on top and acute angle straight theta with straight k with hat on top, then find the components of straight a with rightwards arrow on top and the angle straight theta.

    Solution

    Let straight a with rightwards arrow on top space equals space straight a subscript 1 straight i with hat on top space plus space straight a subscript 2 straight j with hat on top space plus space straight a subscript 3 straight k with hat on top
      Since straight a with rightwards arrow on top makes an angle straight pi over 3 with straight i with hat on top
    therefore space space space cos space straight pi over 3 space equals space fraction numerator straight a with rightwards arrow on top. space straight i with hat on top over denominator open vertical bar straight a with rightwards arrow on top close vertical bar. space open vertical bar straight i with hat on top close vertical bar end fraction space space space space rightwards double arrow space space space 1 half space equals space fraction numerator straight a subscript 1 over denominator left parenthesis 1 right parenthesis thin space left parenthesis 1 right parenthesis end fraction space space space space space space open square brackets because space straight a with rightwards arrow on top space is space straight a space unit space vector close square brackets
rightwards double arrow space space space space space straight a subscript 1 space equals space 1 half
    Again straight a with rightwards arrow on top makes an angle straight pi over 4 space with space straight j with hat on top
    therefore space space cos space straight pi over 4 space equals space fraction numerator straight a with rightwards arrow on top. space straight j with hat on top over denominator open vertical bar straight a with rightwards arrow on top close vertical bar. space open vertical bar straight j with hat on top close vertical bar end fraction space space space rightwards double arrow space space space space fraction numerator 1 over denominator square root of 2 end fraction space equals space fraction numerator straight a subscript 2 over denominator left parenthesis 1 right parenthesis thin space left parenthesis 1 right parenthesis end fraction space space rightwards double arrow space space space space straight a subscript 2 space equals space fraction numerator 1 over denominator square root of 2 end fraction
    Since straight a with rightwards arrow on top is a unit vector
    therefore space space space space straight a subscript 1 squared plus straight a subscript 2 squared plus straight a subscript 3 squared space equals space 1
    therefore space space space 1 fourth plus 1 half plus straight a subscript 3 squared space equals space 1 space space space space space space space space space space space space space space space space space space open square brackets because space space straight a subscript 1 space equals space 1 half comma space straight a subscript 2 space equals fraction numerator 1 over denominator square root of 2 end fraction close square brackets
rightwards double arrow space space space space straight a subscript 3 squared space equals space 1 fourth space space space space space rightwards double arrow space space space space straight a subscript 3 space equals plus-or-minus 1 half
    Now straight theta is the angle between straight a with rightwards arrow on top space and space straight k with hat on top
    therefore space space space cos space straight theta space equals space fraction numerator straight a with rightwards arrow on top. space straight k with hat on top over denominator open vertical bar straight a with rightwards arrow on top close vertical bar. space stack open vertical bar straight k close vertical bar with hat on top end fraction space equals space fraction numerator straight a subscript 3 over denominator left parenthesis 1 right parenthesis thin space left parenthesis 1 right parenthesis end fraction space equals plus-or-minus 1 half
therefore space space space space straight theta space equals space straight pi over 3 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space 0 space less or equal than space straight theta space less or equal than space straight pi space and space straight theta space is space acute close square brackets

    Question 448
    CBSEENMA12034124

    Let straight a with rightwards arrow on top space equals space 4 straight i with hat on top space plus space 5 straight j with hat on top space minus space straight k with hat on top comma space straight b with rightwards arrow on top space equals space straight i with hat on top minus 4 straight j with hat on top plus space 5 straight k with hat on top space and space straight c with rightwards arrow on top space equals 3 straight i with hat on top plus straight j with hat on top minus straight k with hat on top. space Find a vector straight d with rightwards arrow on top which is perpendicular to both straight a with rightwards arrow on top space and space straight b with rightwards arrow on top space and space straight d with rightwards arrow on top. space straight c with rightwards arrow on top space equals space 21.

    Solution
    straight a with rightwards arrow on top space equals space 4 straight i with hat on top space plus space 5 straight j with hat on top space minus space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space straight i with hat on top space minus space 4 straight j with hat on top space plus space 5 straight k with hat on top comma space straight c with rightwards arrow on top space equals space 3 straight i with hat on top space plus space straight j with hat on top space minus space straight k with hat on top
    Let  straight d with rightwards arrow on top space equals space straight d subscript 1 straight i with hat on top plus straight d subscript 2 straight j with hat on top plus straight d subscript 3 straight k with hat on top
    Since straight d with rightwards arrow on top is perpendicular to straight a with rightwards arrow on top space and space straight b with rightwards arrow on top
    therefore space space straight d with rightwards arrow on top space. space straight a with rightwards arrow on top space equals space 0 space space and space straight d with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0
therefore space space space space 4 space straight d subscript 1 space plus space 5 space straight d subscript 2 space minus space straight d subscript 3 space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
    and   straight d subscript 1 minus 4 straight d subscript 2 plus 5 straight d subscript 3 space equals 0                                                                     ...(2)
    Again,                  straight d with rightwards arrow on top. space straight i with hat on top space equals space 21
    rightwards double arrow space space space 3 space straight d subscript 1 space plus space straight d subscript 2 space minus straight d subscript 3 space equals space 21                                                                 ...(3)
    Subtracting (3) from (1), we get, 
                              straight d subscript 1 plus 4 space straight d subscript 2 space equals space minus 21                                                       ...(4)               
    Multiply (2) by 1 and (3) by 5, we get.
        straight d subscript 1 minus 4 space straight d subscript 2 plus 5 space straight d subscript 3 space equals 0
       15 space straight d subscript 1 space plus space 5 space straight d subscript 2 space minus space 5 space straight d subscript 3 space equals space 105
    Adding,      16 space straight d subscript 1 space plus space straight d subscript 2 space equals space 105                                                           ...(5)
    therefore space space space space 64 space straight d subscript 1 space plus space 4 space straight d subscript 2 space equals space 420                                                                      
    Subtracting it from (4), we get,
                        negative 63 space straight d subscript 1 space equals space minus 441 space space space space space space space space space space space rightwards double arrow space space space space straight d subscript 1 space equals space 7
    From (5),      112 plus straight d subscript 2 space equals space 105 space space space space space space space rightwards double arrow space space space space space space straight d subscript 2 space equals space minus 7
    From (1), 28 minus 35 space minus straight d subscript 3 space equals 0 space space space space space space space space space space space space space space space space rightwards double arrow space space space straight d subscript 3 space equals space minus 7
    therefore space space space space straight d with rightwards arrow on top space equals 7 straight i with hat on top space minus space 7 straight j with hat on top space minus space 7 straight k with hat on top
    Question 449
    CBSEENMA12034125

    Let straight a with rightwards arrow on top space equals straight i with hat on top plus 4 straight j with hat on top plus 2 straight k with hat on top comma space space straight b with rightwards arrow on top space equals space 3 straight i with hat on top space minus space 2 straight j with hat on top space plus space 7 straight k with hat on top space and space straight c with rightwards arrow on top space equals space 2 straight i with hat on top minus straight j with hat on top minus 4 straight k with hat on top. Find a vector straight d with rightwards arrow on top which is perpendicular to both straight a with rightwards arrow on top space and space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top. space straight d with rightwards arrow on top space equals space 15.

    Solution

    Here straight a with rightwards arrow on top space equals space straight i with hat on top plus 4 straight j with hat on top plus 2 straight k with hat on top comma space space straight b with rightwards arrow on top space equals 3 straight i with hat on top minus 2 straight j with hat on top plus 7 straight k with hat on top comma space straight c with rightwards arrow on top space equals space 2 straight i with hat on top minus straight j with hat on top minus 4 straight k with hat on top
    Let straight d with rightwards arrow on top space equals space straight d subscript 1 straight i with hat on top plus straight d subscript 2 straight j with hat on top plus straight d subscript 3 straight k with hat on top
    Since straight d with rightwards arrow on top is perpendicular to straight a with rightwards arrow on top space and space straight b with rightwards arrow on top
    therefore space space straight d with rightwards arrow on top. space straight a with rightwards arrow on top space equals 0 space space space and space straight d with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0
    therefore space space space space space straight d subscript 1 plus 4 straight d subscript 2 space plus space 2 straight d subscript 3 space equals space 0                                               ...(1)
    and    3 space straight d subscript 1 space minus space 2 space straight d subscript 2 space plus space 7 space straight d subscript 3 space equals space 0                                      ...(2)
    Again straight c with rightwards arrow on top. straight d with rightwards arrow on top space equals space 15
    therefore space space space 2 space straight d subscript 1 space minus space straight d subscript 2 space plus space 4 space straight d subscript 3 space equals space 15                                         ...(3)
    Multiplying (1) by 7 and (2) by -2, we get,
                      7 space straight d subscript 1 space plus space 28 space straight d subscript 2 space plus space 14 space straight d subscript 3 space equals space 0
minus 6 space straight d subscript 1 space plus space 4 space straight d subscript 2 space minus space 14 space straight d subscript 3 space equals space 0
    Adding,                 straight d subscript 1 space plus space 32 space straight d subscript 2 space equals space 0                               ...(4)
    Multiplying (1) by 2  and (3) by -1, we get,
                   2 space straight d subscript 1 plus space 8 space straight d subscript 2 space plus space 4 space straight d subscript 3 space equals space 0
minus 2 space straight d subscript 1 plus space straight d subscript 2 space minus space 4 space straight d subscript 3 space equals space 0
    Adding,          9 space straight d subscript 2 space equals space minus 15 comma space space space space space therefore space space straight d subscript 2 space equals space minus 15 over 9 space equals space minus 5 over 3
    From (4),   straight d subscript 1 minus 160 over 3 space equals space 0 comma            therefore space space space straight d subscript 1 space equals space 160 over 3
    From (1),    160 over 3 minus 20 over 3 plus 2 space straight d subscript 3 space equals space 0 comma space space space space space space therefore space space space 2 space straight d subscript 3 space equals space 20 over 3 minus 160 over 3
    therefore space space 2 space straight d subscript 3 space equals space fraction numerator 20 minus 160 over denominator 3 end fraction space equals space minus 140 over 3 space space space space space space rightwards double arrow space space space space straight d subscript 3 space equals space minus 70 over 3
    therefore space space required space vector space straight d with rightwards arrow on top space equals space 160 over 3 straight i with hat on top minus 5 over 3 straight j with hat on top space minus 70 over 3 straight k with hat on top
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space 5 over 3 left parenthesis 32 space straight i with hat on top space minus space straight j with hat on top space minus space 14 space straight k with hat on top right parenthesis

     

    Question 450
    CBSEENMA12034126

    Let straight a with rightwards arrow on top space equals straight i with hat on top space minus straight j with hat on top comma space straight b with rightwards arrow on top space equals space 3 straight j with hat on top space minus space straight k with hat on top space and space straight c with rightwards arrow on top space equals 7 straight i with hat on top space minus space straight k with hat on top. Find a vector straight d with rightwards arrow on top which is perpendicular to both straight a with rightwards arrow on top space and space straight b with rightwards arrow on top and straight c with rightwards arrow on top. straight d with rightwards arrow on top space equals space 1

    Solution

    Here straight a with rightwards arrow on top space equals straight i with hat on top space minus space straight j with hat on top comma space straight b with rightwards arrow on top space equals space 3 straight j with hat on top space minus space straight k with hat on top comma space space straight c with rightwards arrow on top space equals space 7 straight i with hat on top space minus space straight k with hat on top
    Let straight d with rightwards arrow on top space equals straight d subscript 1 straight i with hat on top space plus space straight d subscript 2 straight j with hat on top space plus space straight d subscript 3 straight k with hat on top
    Since straight d with rightwards arrow on top is perpendicular to straight a with rightwards arrow on top space and space straight b with rightwards arrow on top
    therefore space space space space straight d with rightwards arrow on top. space straight a with rightwards arrow on top space equals space 0 space space space and space straight d with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0
therefore space space space space space straight d subscript 1 space minus space straight d subscript 2 space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
    and     3d2 – d3 = 0    ...(2)
    Also,         straight c with rightwards arrow on top. space straight d with rightwards arrow on top space equals space 1 space space space space space space space space space rightwards double arrow space space space space 7 space straight d subscript 1 space minus space straight d subscript 3 space equals space 1               ...(3)

    Multiplying (1) by 3 and (2) by 1, we get,
    3d1 – 3d2 = 0
    3d2 – d3 = 0
    Adding, 3d1 – d3 = 0    ...(4)
    Subtracting (4) from (3), we get,
                               4 straight d subscript 1 space equals space 1                         rightwards double arrow space space space straight d subscript 1 space equals 1 fourth
    From (1),  1 fourth minus straight d subscript 2 space equals space 0                             rightwards double arrow space space space straight d subscript 2 space equals space 1 fourth
    From (2),  3 over 4 minus straight d subscript 3 space equals space 0 space space space space space space space rightwards double arrow space space space space straight d subscript 3 space equals space 3 over 4
    therefore space space straight d with rightwards arrow on top space equals space 1 fourth straight i with hat on top space plus 1 fourth straight j with hat on top space plus space 3 over 4 straight k with hat on top
therefore space space space straight d with rightwards arrow on top space equals space 1 fourth left parenthesis straight i with hat on top space plus space straight j with hat on top space plus space 3 space straight k with hat on top right parenthesis

    Question 451
    CBSEENMA12034127

    Dot product of a vector with vectors 2 straight i with hat on top space plus space 3 straight j with hat on top space plus space straight k with hat on top comma space space 4 straight i with hat on top space plus space straight j with hat on top space and space straight i with hat on top space minus space 3 straight j with hat on top space minus space 7 straight k with hat on top are respectively 9, 7 and 6. Find the vector.

    Solution

    Let straight r with rightwards arrow on top space equals space straight x straight i with hat on top space plus space straight y straight j with hat on top space plus space straight z straight k with hat on top be required vector. 
     From given conditions,
    left parenthesis straight x straight i with hat on top space plus space straight y straight j with hat on top plus straight z straight k with hat on top right parenthesis. space left parenthesis 2 straight j with hat on top plus 3 straight j with hat on top plus straight k with hat on top right parenthesis space equals space 9 space space space rightwards double arrow space space space 2 straight x plus 3 straight y plus straight z space equals space 9               ...(1)
    left parenthesis straight x straight i with hat on top space plus space straight y straight j with hat on top space plus straight z straight k with hat on top right parenthesis. space left parenthesis 4 straight i with hat on top plus straight j with hat on top right parenthesis space equals space 7 space space space space space space space rightwards double arrow space space space 4 straight x plus straight y space equals 7                             ...(2)
    left parenthesis straight x straight i with hat on top plus space straight y straight j with hat on top space plus space straight z straight k with hat on top right parenthesis. space left parenthesis straight i with hat on top minus 3 straight j with hat on top minus 7 straight k with hat on top right parenthesis space equals 6 space space space space rightwards double arrow space space straight x minus 3 straight y minus 7 straight z space equals space 6                ...(3)
    Multiplying (1) by 7 and (3) by 1, we get,
    14x + 21 y + 7z = 63
    x – 3y – 7z = 6
    Adding, we get.
    15x +18y = 69 or 5x + 6y = 23    …(4)
    Multiplying (2) by 6 and (4) by 1, we get,
    24x + 6y = 42    ...(5)
    5x + 6y = 23    ...(6)
    Subtracting (6) from (5), we get,
    19x = 19 or x = 1
    Putting x = 1 in (2), we get,
    4 + y = 7 or y = 3
    Putting x = 1, y = 3 in (1), we get,
    2 + 9 + z = 9 or z = – 2
    therefore space space space space straight r with rightwards arrow on top space equals space straight i with hat on top space plus space 3 straight j with hat on top minus 2 straight k with hat on top space is space required space vector.

    Question 452
    CBSEENMA12034128

    Dot product of a vector with vectors 3 space straight i with hat on top minus 5 space straight k with hat on top comma space space space 2 straight i with hat on top plus space 7 space straight j with hat on top space and space straight i with hat on top plus straight j with hat on top plus straight k with hat on top are respectively – 1, 6 and 5. Find the vector.

    Solution

    Let straight r with rightwards arrow on top space equals space straight x straight i with hat on top space plus space straight y straight j with hat on top plus straight z straight k with hat on top be required vector.
    From given conditions,
                left parenthesis straight x straight i with hat on top plus straight y straight j with hat on top plus straight z straight k with hat on top right parenthesis. space left parenthesis 3 straight i with hat on top space minus 5 straight k with hat on top right parenthesis space equals space minus 1 space space space space space space space rightwards double arrow space space space 3 straight x minus 5 straight z space equals space minus 1         ...(1)
                left parenthesis straight x straight i with hat on top plus straight y straight j with hat on top plus straight z straight k with hat on top right parenthesis. space left parenthesis 2 straight i with hat on top plus 7 straight j with hat on top right parenthesis space equals space 6 space space space rightwards double arrow space space space 2 straight x plus 7 straight y space equals space 6                       ...(2)
                left parenthesis straight x straight i with hat on top plus straight y straight j with hat on top plus straight z straight k with hat on top right parenthesis. space left parenthesis straight i with hat on top plus straight j with hat on top plus straight k with hat on top right parenthesis space equals space 5 space space space rightwards double arrow space space space straight x plus straight y plus straight z space equals space 5                     ...(3)
            7 space cross times space left parenthesis 3 right parenthesis space minus space left parenthesis 2 right parenthesis space gives comma space       5 straight x plus 7 straight z space equals 29                                          ...(4)
    Multiplying (2) by 7 and (4) by 5, we get,
             21 x - 35 z = -7 
              25 x+35 z = 145
    Adding these equation, 46x = 138  rightwards double arrow space space straight x space equals space 3
    therefore space space from space left parenthesis 2 right parenthesis comma space 6 plus 7 straight y space equals space 6 space space space space rightwards double arrow space space space 7 straight y space equals space 0 space space space space rightwards double arrow space space straight y space equals space 0
From space left parenthesis 1 right parenthesis comma space space 9 space minus space 5 straight z space equals space minus 1 space space space space rightwards double arrow space space space minus 5 straight z space equals space minus 10 space rightwards double arrow space straight z space equals space 2
therefore space space space space straight r with rightwards arrow on top space equals space 3 straight i with hat on top plus 2 straight k with hat on top

    Question 453
    CBSEENMA12034129

    Find the scalar components of a unit vector which is perpendicular to the vectors straight i with hat on top plus 2 space straight j with hat on top space minus space straight k with hat on top space space and space space 3 straight i with hat on top minus straight j with hat on top plus 2 space straight k with hat on top.

    Solution

    Let straight r with rightwards arrow on top space equals straight x straight i with hat on top plus straight y straight j with hat on top plus straight z straight k with hat on top                      ...(1)
    be the unit vector which is perpendicular to the vectors
              straight a with rightwards arrow on top space equals straight i with hat on top space plus space 2 space straight j with hat on top space minus space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space 3 straight i with hat on top space minus straight j with hat on top space plus 2 straight k with hat on top
    therefore space space space space space straight x squared plus straight y squared plus straight z squared space equals 1                                                ...(2)
              straight x plus 2 straight y minus straight z space equals space 0                                                  ...(3)
               3 straight x minus straight y plus 2 straight z space equals space 0                                              ...(4)
    Multiplying (3) by 1 and (4) by 2, we get,
    x + 2y – z = 0
    6x – 2y + 4z = 0
    Adding,    7 straight x plus 3 straight z space equals space 0 comma space space space space therefore space space space straight z space equals space minus 7 over 3 straight x
    Multiplying (3) by 2 and (4) by 1, we get,
    2x + 4y – 2z = 0
    3x – y + 2z = 0
    Adding,       5 straight x plus 3 straight y space equals space 0 space space space space space space rightwards double arrow space space space straight y space equals space minus fraction numerator 5 straight x over denominator 3 end fraction
    Putting     straight y space equals space minus fraction numerator 5 straight x over denominator 3 end fraction comma space space space straight z space equals space minus fraction numerator 7 straight x over denominator 3 end fraction space in space left parenthesis 1 right parenthesis comma space we space get comma
              straight x squared plus 25 over 9 straight x squared plus 49 over 9 straight x squared space equals space 1 space space space space space space rightwards double arrow space space space straight x space equals space space plus-or-minus fraction numerator 3 over denominator square root of 83 end fraction
    therefore space space space straight x squared space equals space 9 over 83 space space space space space space space rightwards double arrow space space space straight x space equals space plus-or-minus fraction numerator 3 over denominator square root of 83 end fraction
therefore space space space straight y space equals plus-or-minus fraction numerator 5 over denominator square root of 83 end fraction comma space space straight z space equals space plus-or-minus fraction numerator 7 over denominator square root of 83 end fraction
therefore space space space required space scalar space components space are
space space space space space space space space space space space space space fraction numerator 3 over denominator square root of 83 end fraction comma space minus fraction numerator 5 over denominator square root of 83 end fraction comma space minus fraction numerator 7 over denominator square root of 83 end fraction space space space or space space space minus fraction numerator 3 over denominator square root of 83 end fraction comma space fraction numerator 5 over denominator square root of 83 end fraction comma space fraction numerator 7 over denominator square root of 83 end fraction

    Question 454
    CBSEENMA12034130

    If straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top comma show that the angle straight theta between the vectors straight b with rightwards arrow on top space and space straight c with rightwards arrow on top is given by
    cos space straight theta space equals space fraction numerator straight a squared minus straight b squared minus straight c squared over denominator 2 space open vertical bar straight b with rightwards arrow on top close vertical bar space open vertical bar straight c with rightwards arrow on top close vertical bar end fraction

    Solution

    Here
                      straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top space space equals 0 with rightwards arrow on top
    therefore space space space straight a with rightwards arrow on top space space equals space minus left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis                                                 ...(1)
    therefore space space space straight a squared space equals space straight a with rightwards arrow on top. space straight a with rightwards arrow on top space equals space open curly brackets negative left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis close curly brackets space. space left curly bracket negative left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis right curly bracket space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
                 equals space left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis. space left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space equals space straight b with rightwards arrow on top. straight b with rightwards arrow on top plus straight b with rightwards arrow on top. straight c with rightwards arrow on top plus straight c with rightwards arrow on top. straight b with rightwards arrow on top space plus straight c with rightwards arrow on top. straight c with rightwards arrow on top
equals space straight b with rightwards arrow on top. straight b with rightwards arrow on top space plus straight b with rightwards arrow on top. space straight c with rightwards arrow on top plus straight b with rightwards arrow on top. straight c with rightwards arrow on top plus straight c with rightwards arrow on top. straight c with rightwards arrow on top space equals space straight b with rightwards arrow on top. straight b with rightwards arrow on top plus 2 left parenthesis straight b with rightwards arrow on top minus straight c with rightwards arrow on top right parenthesis plus straight c with rightwards arrow on top. straight c with rightwards arrow on top
    therefore space space space space space straight a squared space equals space straight b squared plus 2 space open vertical bar straight b with rightwards arrow on top close vertical bar space open vertical bar straight c with rightwards arrow on top close vertical bar space cos space straight theta space plus space straight c squared
    space therefore space space 2 space open vertical bar straight b with rightwards arrow on top close vertical bar space open vertical bar straight c with rightwards arrow on top close vertical bar space cos space straight theta space equals straight a squared minus straight b squared minus straight c squared
space therefore space space space space cos space straight theta space equals space fraction numerator straight a squared minus straight b squared minus straight c squared over denominator 2 space open vertical bar straight b with rightwards arrow on top close vertical bar space open vertical bar straight c with rightwards arrow on top close vertical bar end fraction

    Question 455
    CBSEENMA12034131

    If straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top space equals 0 with rightwards arrow on top space and space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 3 comma space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 5 comma space space open vertical bar straight c with rightwards arrow on top close vertical bar space equals 7 comma show that the angle between straight a with rightwards arrow on top space and space straight b with rightwards arrow on top is 60°.

    Solution

    Let straight theta be angle between straight a with rightwards arrow on top space and space straight b with rightwards arrow on top
    Now  straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top space space space space space space rightwards double arrow space space space straight a with rightwards arrow on top plus straight b with rightwards arrow on top space equals space minus straight c with rightwards arrow on top
    therefore space space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space equals left parenthesis negative straight c with rightwards arrow on top right parenthesis. space left parenthesis straight c with rightwards arrow on top right parenthesis
therefore space space straight a with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top. space straight c with rightwards arrow on top
therefore space space space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space straight a with rightwards arrow on top. straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space open vertical bar straight c with rightwards arrow on top close vertical bar squared
therefore space space space left parenthesis 3 right parenthesis squared plus straight a space straight b space cos space straight theta space plus space straight a space straight b space cos space straight theta space plus space left parenthesis 5 right parenthesis squared space equals space left parenthesis 7 right parenthesis squared
                                                                        open square brackets because space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 3 comma space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 5 comma space space space open vertical bar straight c with rightwards arrow on top close vertical bar space space equals 7 close square brackets
    therefore space space 9 space plus space 2 space straight a space straight b space cos space straight theta plus 25 space equals space 49
therefore space space 2 space straight a space straight b space cos space straight theta space equals space 15 space space space space space rightwards double arrow space space space 2 space left parenthesis 3 right parenthesis thin space left parenthesis 5 right parenthesis space cos space straight theta space equals space 15 space space space space space space space space space space space space open square brackets because space straight a space equals 3 comma space space straight b space equals space 5 close square brackets
therefore space space space cos space straight theta space equals space 1 half space space space rightwards double arrow space space space space space straight theta space equals space 60 degree.

    Question 456
    CBSEENMA12034132

    Let straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top be three vectors of magnitude 5, 3, 1 respectively. If each one is perpendicular to the sum of other two vectors, prove that open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar space equals space square root of 35.

    Solution
    We have
    open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 5 comma space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 3 comma space space open vertical bar straight c with rightwards arrow on top close vertical bar space equals space 1                             ...(1)
    Since straight a with rightwards arrow on top is perpendicular to straight b with rightwards arrow on top plus straight c with rightwards arrow on top,  straight b with rightwards arrow on top is perpendicular to straight c with rightwards arrow on top plus straight a with rightwards arrow on top space and space straight c with rightwards arrow on top is perpendicular to straight a with rightwards arrow on top plus straight b with rightwards arrow on top.
    therefore space space space straight a with rightwards arrow on top. space left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space equals space 0
                                          ...(2)
           straight b with rightwards arrow on top. space left parenthesis straight c with rightwards arrow on top plus straight a with rightwards arrow on top right parenthesis space equals space 0                                           ...(3)
    and  straight c with rightwards arrow on top. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space equals space 0                                         ...(4)
    Now,   open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar squared space equals space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis
                    equals space straight a with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight a with rightwards arrow on top. space left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space plus space straight b with rightwards arrow on top. straight b with rightwards arrow on top space plus space straight b with rightwards arrow on top. space left parenthesis straight c with rightwards arrow on top plus straight a with rightwards arrow on top right parenthesis space plus straight c with rightwards arrow on top. straight c with rightwards arrow on top plus straight c with rightwards arrow on top. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis
equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus straight a with rightwards arrow on top. space left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space plus open vertical bar straight b with rightwards arrow on top close vertical bar squared space plus straight b with rightwards arrow on top. space thin space left parenthesis straight c with rightwards arrow on top plus straight a with rightwards arrow on top right parenthesis space plus space open vertical bar straight c with rightwards arrow on top close vertical bar squared space plus straight c with rightwards arrow on top. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis
space equals space 25 plus 0 plus 9 plus 0 plus 1 plus 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis comma space left parenthesis 2 right parenthesis comma space left parenthesis 3 right parenthesis comma space left parenthesis 4 right parenthesis close square brackets
therefore space space space space open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar squared space equals space 35
therefore space space space space space space open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar space equals space square root of 35.
    Question 457
    CBSEENMA12034133

    If straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top are three mutually perpendicular vectors of equal magnitude find the angle between straight a with rightwards arrow on top space and space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis.

    Solution

    We have
    open vertical bar straight a with rightwards arrow on top close vertical bar space equals open vertical bar straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight c with rightwards arrow on top close vertical bar space and space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space equals space straight c with rightwards arrow on top. space straight a with rightwards arrow on top space equals 0                     ...(1)
    Now open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar squared space space equals space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis squared space equals left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis.
                        equals space straight a with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight c with rightwards arrow on top space equals open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared plus space open vertical bar straight c with rightwards arrow on top close vertical bar squared space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space open vertical bar straight a with rightwards arrow on top close vertical bar squared space equals 3 space open vertical bar straight a with rightwards arrow on top close vertical bar squared space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets space
therefore space space space open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar space equals space square root of 3 space open vertical bar straight a with rightwards arrow on top close vertical bar space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis space
    Let straight theta be angle between <pre>uncaught exception: <b>file_put_contents(/home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/web/../../../../../../formulas/5a/9e/e6cfd017e47b71817b27babff0d8.ini): failed to open stream: Permission denied (errno: 2) in /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/sys/io/File.class.php at line #12file_put_contents(/home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/web/../../../../../../formulas/5a/9e/e6cfd017e47b71817b27babff0d8.ini): failed to open stream: Permission denied</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/sys/io/File.class.php line 12<br />#0 [internal function]: _hx_error_handler(2, 'file_put_conten...', '/home/config_ad...', 12, Array)
#1 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/sys/io/File.class.php(12): file_put_contents('/home/config_ad...', 'mml=<math xmlns...')
#2 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/util/sys/Store.class.php(48): sys_io_File::saveContent('/home/config_ad...', 'mml=<math xmlns...')
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/FolderTreeStorageAndCache.class.php(112): com_wiris_util_sys_Store->write('mml=<math xmlns...')
#4 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/RenderImpl.class.php(231): com_wiris_plugin_impl_FolderTreeStorageAndCache->codeDigest('mml=<math xmlns...')
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(59): com_wiris_plugin_impl_RenderImpl->computeDigest(NULL, Array)
#6 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#7 {main}</pre>
    therefore space space space straight a with rightwards arrow on top. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space equals space open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight a with rightwards arrow on top plus space straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar space cos space straight theta
therefore space space space space space space space space space space space space straight a with rightwards arrow on top. space straight a with rightwards arrow on top space equals space open vertical bar straight a with rightwards arrow on top close vertical bar space. space square root of 3 space open vertical bar straight a with rightwards arrow on top close vertical bar space space cos space straight theta space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis comma space left parenthesis 2 right parenthesis close square brackets
rightwards double arrow space space space open vertical bar straight a with rightwards arrow on top close vertical bar squared space equals space square root of 3 space space open vertical bar straight a with rightwards arrow on top close vertical bar squared space cos space straight theta space space rightwards double arrow space space cos space straight theta space equals space fraction numerator 1 over denominator square root of 3 end fraction
therefore space space space space straight theta space equals space cos to the power of negative 1 end exponent open parentheses fraction numerator 1 over denominator square root of 3 end fraction close parentheses.
space space
                     

    Question 458
    CBSEENMA12034134

    If straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top are mutually perpendicular vectors of equal magnitude, show that they are equally inclined to the vector left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis

    Solution

    We have
                     open vertical bar straight a with rightwards arrow on top close vertical bar space equals space open vertical bar straight b with rightwards arrow on top close vertical bar space equals open vertical bar straight c with rightwards arrow on top close vertical bar space and space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space equals space straight c with rightwards arrow on top. space straight a with rightwards arrow on top space equals space 0                 ...(1)
     Now space open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar squared space equals space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis squared space equals space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top plus space straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis
space space space space space space space space space space space space space space space space space space space space space space equals space straight a with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight c with rightwards arrow on top space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus open vertical bar straight b with rightwards arrow on top close vertical bar squared plus open vertical bar straight c with rightwards arrow on top close vertical bar squared space space space space space space space space left square bracket because space of space left parenthesis 1 right parenthesis right square bracket
space space space space space space space space space space space space space space space space space space space space space space space equals open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space open vertical bar straight a with rightwards arrow on top close vertical bar squared space equals space 3 space open vertical bar straight a with rightwards arrow on top close vertical bar squared space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space left square bracket because space of space left parenthesis 1 right parenthesis right square bracket
therefore space space space open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar space equals space square root of 3 space open vertical bar straight a with rightwards arrow on top close vertical bar space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis
    Let straight theta be angle between <pre>uncaught exception: <b>file_put_contents(/home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/web/../../../../../../formulas/5a/9e/e6cfd017e47b71817b27babff0d8.ini): failed to open stream: Permission denied (errno: 2) in /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/sys/io/File.class.php at line #12file_put_contents(/home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/web/../../../../../../formulas/5a/9e/e6cfd017e47b71817b27babff0d8.ini): failed to open stream: Permission denied</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/sys/io/File.class.php line 12<br />#0 [internal function]: _hx_error_handler(2, 'file_put_conten...', '/home/config_ad...', 12, Array)
#1 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/sys/io/File.class.php(12): file_put_contents('/home/config_ad...', 'mml=<math xmlns...')
#2 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/util/sys/Store.class.php(48): sys_io_File::saveContent('/home/config_ad...', 'mml=<math xmlns...')
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/FolderTreeStorageAndCache.class.php(112): com_wiris_util_sys_Store->write('mml=<math xmlns...')
#4 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/RenderImpl.class.php(231): com_wiris_plugin_impl_FolderTreeStorageAndCache->codeDigest('mml=<math xmlns...')
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(59): com_wiris_plugin_impl_RenderImpl->computeDigest(NULL, Array)
#6 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#7 {main}</pre>
    therefore space space straight a with rightwards arrow on top left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space equals space open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar space cos space straight theta
therefore space space space space space space space space space straight a with rightwards arrow on top. space straight a with rightwards arrow on top space equals space open vertical bar straight a with rightwards arrow on top close vertical bar. space square root of 3 space open vertical bar straight a with rightwards arrow on top close vertical bar space cos space straight theta space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis comma space left parenthesis 2 right parenthesis close square brackets
rightwards double arrow space space space space open vertical bar straight a with rightwards arrow on top close vertical bar squared space equals space square root of 3 space open vertical bar straight a with rightwards arrow on top close vertical bar squared space cos space straight theta space space space space space rightwards double arrow space space space cos space straight theta space equals space fraction numerator 1 over denominator square root of 3 end fraction
therefore space space space space space space space straight theta space equals space cos to the power of negative 1 end exponent open parentheses fraction numerator 1 over denominator square root of 3 end fraction close parentheses.
    Let straight theta be the angle between
     straight b with rightwards arrow on top space and space straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top
      therefore space space space straight b with rightwards arrow on top space. space space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space equals space open vertical bar straight b with rightwards arrow on top close vertical bar space open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar space cos space straight ϕ
therefore space space space space straight b with rightwards arrow on top. space straight b with rightwards arrow on top space equals space open vertical bar straight b with rightwards arrow on top close vertical bar space. space square root of 3 space open vertical bar straight b with rightwards arrow on top close vertical bar space cos space straight ϕ space space space space space space space left square bracket because space space open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar space equals space square root of 3 space open vertical bar straight b with rightwards arrow on top close vertical bar right square bracket
rightwards double arrow space space space space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space square root of 3 space open vertical bar straight b with rightwards arrow on top close vertical bar squared space cos space straight ϕ space space space space rightwards double arrow space space space space cos space straight ϕ space equals space fraction numerator 1 over denominator square root of 3 end fraction
therefore space space space space space space straight ϕ space equals space cos space to the power of negative 1 end exponent space open parentheses fraction numerator 1 over denominator square root of 3 end fraction close parentheses
    Let straight psi be angle between straight c with rightwards arrow on top space and space straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top
    therefore space space space space straight c with rightwards arrow on top. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space equals space open vertical bar straight c with rightwards arrow on top close vertical bar space open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar space cos space straight psi
    therefore space space straight c with rightwards arrow on top. space straight c with rightwards arrow on top space equals open vertical bar straight c with rightwards arrow on top close vertical bar. space square root of 3 space open vertical bar straight c with rightwards arrow on top close vertical bar space cos space straight psi
rightwards double arrow space space space space space space space space straight psi space equals space cos to the power of negative 1 end exponent space open parentheses fraction numerator 1 over denominator square root of 3 end fraction close parentheses
therefore space space space space space space space straight theta space equals straight ϕ space equals straight psi
therefore space space space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top space are space equally space inclined space to space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis.

    Question 459
    CBSEENMA12034135

    If straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top are unit vectors such that straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top space equals space 0, then find the value of straight a with rightwards arrow on top. straight b with rightwards arrow on top plus straight b with rightwards arrow on top. straight c with rightwards arrow on top plus straight c with rightwards arrow on top. straight a with rightwards arrow on top.

    Solution

    Here
                   straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top space equals 0 with rightwards arrow on top
    therefore space space space straight a with rightwards arrow on top plus straight b with rightwards arrow on top space equals negative straight c with rightwards arrow on top                                 ...(1)
    therefore space space space straight a with rightwards arrow on top. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space equals space minus straight a with rightwards arrow on top. straight c with rightwards arrow on top
rightwards double arrow space space space straight a with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space minus straight a with rightwards arrow on top. space straight c with rightwards arrow on top
rightwards double arrow space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus straight a with rightwards arrow on top. straight b with rightwards arrow on top plus straight a with rightwards arrow on top. straight c with rightwards arrow on top space equals 0
therefore space space space 1 plus straight a with rightwards arrow on top. straight b with rightwards arrow on top plus straight a with rightwards arrow on top. straight c with rightwards arrow on top space equals 0 space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because straight a with rightwards arrow on top space is space straight a space unit space vector close square brackets
From space left parenthesis 1 right parenthesis comma space space straight b with rightwards arrow on top. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space equals negative straight b with rightwards arrow on top. space straight c with rightwards arrow on top space space space rightwards double arrow space space space straight b with rightwards arrow on top. space stack straight a space with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight b with rightwards arrow on top space equals space minus straight b with rightwards arrow on top. space straight c with rightwards arrow on top
rightwards double arrow space space space straight b with rightwards arrow on top. space straight a with rightwards arrow on top plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space plus space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space equals space 0
rightwards double arrow space space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space plus 1 plus space straight b with rightwards arrow on top space. space straight c with rightwards arrow on top space equals space 0 space space space space space space space space space space space space space space space space space space open square brackets because space straight b with rightwards arrow on top space is space straight a space unit space vector close square brackets
therefore space space space space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space equals space minus 1 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 3 right parenthesis
    Again from (1), straight c with rightwards arrow on top. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space equals space minus straight c with rightwards arrow on top. space straight c with rightwards arrow on top
    therefore space space space straight c with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight b with rightwards arrow on top space equals space minus open vertical bar straight c with rightwards arrow on top close vertical bar squared space space space space rightwards double arrow space space space space straight c with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight b with rightwards arrow on top space plus space open vertical bar straight c with rightwards arrow on top close vertical bar squared space equals space 0
rightwards double arrow space space straight c with rightwards arrow on top. space straight a with rightwards arrow on top space plus straight c with rightwards arrow on top. space straight b with rightwards arrow on top space plus 1 space space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space straight c with rightwards arrow on top space is space straight a space unit space vector close square brackets
rightwards double arrow space space straight c with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight b with rightwards arrow on top space equals space minus 1
    Adding (2), (3) and (4), we get
                     2 left parenthesis straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight a with rightwards arrow on top right parenthesis space equals space minus 3 space space space space space space space space space space space space space space space space space space space space space open square brackets because space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space etc. close square brackets
therefore space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight a with rightwards arrow on top space equals space minus 3 over 2

    Question 460
    CBSEENMA12034136

    Three vectors straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top satisfy the condition straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top space equals 0 with rightwards arrow on top. Evaluate the quantity straight mu space equals space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus straight b with rightwards arrow on top. space straight c with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight a with rightwards arrow on top comma space if space open vertical bar straight a with rightwards arrow on top close vertical bar space equals 1 comma space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 4 space and space open vertical bar straight c with rightwards arrow on top close vertical bar space equals space 2.

    Solution

    Here
            straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top
    therefore space space space space space straight a with rightwards arrow on top plus straight b with rightwards arrow on top space equals space minus straight c with rightwards arrow on top                                                       ...(1)
    therefore space space space straight a with rightwards arrow on top. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space equals space minus straight a with rightwards arrow on top. space straight c with rightwards arrow on top
rightwards double arrow space space space space space straight a with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space minus straight a with rightwards arrow on top. space straight c with rightwards arrow on top
rightwards double arrow space space space space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight c with rightwards arrow on top space equals space 0
therefore space space space space 1 plus straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight c with rightwards arrow on top space equals 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 1 close square brackets
therefore space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight c with rightwards arrow on top space equals space minus 1 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis
From space left parenthesis 1 right parenthesis comma space space straight b with rightwards arrow on top. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis equals space minus straight b with rightwards arrow on top. space straight c with rightwards arrow on top space space space rightwards double arrow space space space space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight b with rightwards arrow on top space equals space minus straight b with rightwards arrow on top. space straight c with rightwards arrow on top
rightwards double arrow space space space space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space plus space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space equals space 0
rightwards double arrow space space space space space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space plus space 16 space plus space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 4 close square brackets
therefore space space space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space plus straight b with rightwards arrow on top. space straight c with rightwards arrow on top space equals space minus 16 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 3 right parenthesis space space space space space space
Again space from space left parenthesis 1 right parenthesis comma space straight c with rightwards arrow on top. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space equals space minus straight c with rightwards arrow on top. space straight c with rightwards arrow on top
therefore space space straight c with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight b with rightwards arrow on top space equals space minus space open vertical bar straight c with rightwards arrow on top close vertical bar squared
rightwards double arrow space space straight c with rightwards arrow on top. straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight b with rightwards arrow on top space equals space minus 4 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 4 right parenthesis
                                                                                       open square brackets because space space open vertical bar straight c with rightwards arrow on top close vertical bar space equals space 2 close square brackets
    Adding (2), (3) and (4), we get
                       2 left parenthesis straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight a with rightwards arrow on top right parenthesis space equals space minus 21 space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space etc close square brackets
therefore space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight a with rightwards arrow on top space equals space minus 21 over 2
rightwards double arrow space space space space space space space space space space straight mu space equals space minus 21 over 2

    Question 461
    CBSEENMA12034137

    Let straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top be three vectors such that open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 3 comma space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 4 comma space space open vertical bar straight c with rightwards arrow on top close vertical bar space equals 5 and each one of them being perpendicular to the sum of the other two, find open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar.

    Solution

    We have
       open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 3 comma space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 4 comma space space space open vertical bar straight c with rightwards arrow on top close vertical bar space equals space 5                      ...(1)
    Since straight a with rightwards arrow on top is perpendicular to straight b with rightwards arrow on top plus straight c with rightwards arrow on top comma space straight b with rightwards arrow on top is perpendicular straight c with rightwards arrow on top plus straight a with rightwards arrow on top and straight c with rightwards arrow on top is perpendicular to straight a with rightwards arrow on top plus straight b with rightwards arrow on top.
                   therefore space space space straight a with rightwards arrow on top. space left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space equals space straight b with rightwards arrow on top. space left parenthesis straight c with rightwards arrow on top plus straight a with rightwards arrow on top right parenthesis space equals space straight c with rightwards arrow on top. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space equals space 0
therefore space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight c with rightwards arrow on top space equals space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space equals space straight c with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0 space space space space space space space space... left parenthesis 2 right parenthesis
    Now,   open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar squared space equals space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis
                  equals space straight a with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight c with rightwards arrow on top space plus space straight b with rightwards arrow on top. straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight b with rightwards arrow on top plus space straight c with rightwards arrow on top. space straight c with rightwards arrow on top
space equals open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space left parenthesis straight a with rightwards arrow on top. space straight b with rightwards arrow on top plus space straight a with rightwards arrow on top. space straight c with rightwards arrow on top right parenthesis space plus left parenthesis straight b with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top. space straight c with rightwards arrow on top right parenthesis space plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared plus space left parenthesis straight c with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight b with rightwards arrow on top right parenthesis space plus space open vertical bar straight c with rightwards arrow on top close vertical bar squared space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space
                                             equals space left parenthesis 3 right parenthesis squared plus 0 plus 0 plus left parenthesis 4 right parenthesis squared plus 0 plus left parenthesis 5 right parenthesis squared space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis comma space left parenthesis 2 right parenthesis close square brackets
space equals space 9 plus 16 plus 25 space equals space 50
    therefore space space space open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top close vertical bar space equals space square root of 50 space equals space 5 square root of 2

    Question 462
    CBSEENMA12034138

    If with reference to the right handed system of mutually perpendicular unit vectors straight i with hat on top comma space space straight j with hat on top space and space straight k with hat on top comma space space straight alpha with rightwards arrow on top space equals space 3 straight i with hat on top minus straight j with hat on top comma space space straight beta with rightwards arrow on top space equals 2 straight i with hat on top space plus space straight j with hat on top space minus space 3 space straight k with hat on top comma space then express straight beta with rightwards arrow on top in the form straight beta with rightwards arrow on top space equals space stack straight beta subscript 1 with rightwards arrow on top space plus space straight beta with rightwards arrow on top subscript 2 comma space space where space stack straight beta subscript 1 with rightwards arrow on top space is space parallel space to space straight alpha with rightwards arrow on top space and space stack straight beta subscript 2 with rightwards arrow on top space is perpendicular to straight alpha with rightwards arrow on top.

    Solution

    Here
          straight alpha with rightwards arrow on top space equals space 3 space straight i with hat on top minus straight j with hat on top comma space straight beta with rightwards arrow on top space equals 2 space straight i with hat on top space plus space straight j with hat on top space minus space 3 space straight k with hat on top
    Since stack straight beta subscript 1 with rightwards arrow on top is parallel to straight alpha with rightwards arrow on top
    therefore space space stack straight beta subscript 1 with rightwards arrow on top space equals space straight lambda straight alpha with rightwards arrow on top space where space straight lambda space is space straight a space scalar.
therefore space space stack straight beta subscript 1 with rightwards arrow on top space equals space 3 space straight lambda space straight i with hat on top space minus space straight lambda space straight j with hat on top space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
    Now,       straight beta with rightwards arrow on top space equals space straight beta with rightwards arrow on top subscript 1 space plus space stack straight beta subscript 2 with rightwards arrow on top space space space rightwards double arrow space space space space stack straight beta subscript 2 with rightwards arrow on top space equals space straight beta with rightwards arrow on top space minus stack straight beta subscript 1 with rightwards arrow on top
     therefore space space space stack straight beta subscript 2 with rightwards arrow on top space equals space left parenthesis 2 straight i with hat on top space plus space straight j with hat on top space minus space 3 space straight k with hat on top right parenthesis space minus space left parenthesis 3 space straight lambda space straight i with hat on top space minus space straight lambda space straight j with hat on top right parenthesis
or space space space space stack straight beta subscript 2 with rightwards arrow on top space equals space left parenthesis 2 minus 3 space straight lambda right parenthesis space straight i with hat on top space plus space left parenthesis 1 plus straight lambda right parenthesis straight j with hat on top space minus space 3 space straight k with hat on top space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis
    Since straight beta with rightwards arrow on top subscript 2 is perpendicular to straight alpha with rightwards arrow on top.
    space therefore space space space straight alpha with rightwards arrow on top. space stack straight beta subscript 2 with rightwards arrow on top space equals space 0 space space space space rightwards double arrow space space space 3 space left parenthesis 2 space minus space 3 space straight lambda right parenthesis space minus space left parenthesis negative 1 right parenthesis space left parenthesis 1 plus straight lambda right parenthesis plus left parenthesis 0 right parenthesis left parenthesis negative 3 right parenthesis space equals space 0
therefore space space space 6 minus 9 straight lambda minus 1 minus straight lambda equals space space 0 space rightwards double arrow space space space space 10 space straight lambda space equals space 5 space space space rightwards double arrow space space straight lambda space equals space 1 half
therefore space space space from space left parenthesis 1 right parenthesis comma space space straight beta with rightwards arrow on top subscript 1 space equals space 3 over 2 straight i with hat on top space minus space 1 half straight j with hat on top
    and from (2),  stack straight beta subscript 2 with rightwards arrow on top space equals space open parentheses 2 minus 3 over 2 close parentheses straight i with hat on top space plus space open parentheses 1 plus 1 half close parentheses space straight j with hat on top space minus space 3 space straight k with hat on top
    or               stack straight beta subscript 2 with rightwards arrow on top space equals space 1 half straight i with hat on top space plus 3 over 2 straight j with hat on top space minus space 3 space straight k with hat on top
    therefore space space straight beta with rightwards arrow on top space equals space open parentheses 3 over 2 straight i with hat on top space minus 1 half straight j with hat on top close parentheses space plus space open parentheses 3 over 2 straight i with hat on top space plus space 3 over 2 straight j with hat on top space minus space 3 space straight k with hat on top close parentheses 

    Question 463
    CBSEENMA12034139

    If straight theta is the angle between two vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top, then straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space greater or equal than space 0 only when 

    • 0 less than straight theta less than straight pi over 2
    • 0 less or equal than straight theta less or equal than straight pi over 2
    • 0 less than straight theta less than straight pi
    • 0 less or equal than straight theta less or equal than straight pi

    Solution

    B.

    0 less or equal than straight theta less or equal than straight pi over 2 straight a with rightwards arrow on top. space straight b with rightwards arrow on top space greater or equal than space 0
    only if open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar space cos space straight theta space greater or equal than space 0 comma space
    i.e.  only if cos space straight theta space greater or equal than space space 0 comma
    i.e., only if 0 less or equal than space straight theta space less or equal than space straight pi over 2.
    (B) is correct answer.
    Question 464
    CBSEENMA12034141

    Let straight a with rightwards arrow on top space and space straight b with rightwards arrow on top be two unit vectors and straight theta be the angle between them. Then straight a with rightwards arrow on top plus straight b with rightwards arrow on top is a unit vector if choose the correct answer.

    • straight theta space equals straight pi over 4
    • straight theta space equals space straight pi over 3
    • straight theta space equals space straight pi over 2
    • straight theta space equals fraction numerator 2 straight pi over denominator 3 end fraction

    Solution

    D.

    straight theta space equals fraction numerator 2 straight pi over denominator 3 end fraction

    Since straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are unit vectors.
    therefore space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 1 comma space space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals 1                                  
    Also,  straight theta is angle between straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.
    therefore space space space space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar space cos space straight theta space equals space left parenthesis 1 right parenthesis thin space left parenthesis 1 right parenthesis space cos space straight theta
or space space space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space cos space straight theta space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis
Now space straight a with rightwards arrow on top plus straight b with rightwards arrow on top space is space straight a space unit space vector
    if    open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar space equals space 1
    i.e. if  open parentheses straight a with rightwards arrow on top plus straight b with rightwards arrow on top close parentheses. space left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis space equals space 1
    i.e. if straight a with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus straight b with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top. straight b with rightwards arrow on top space equals 1
    i.e. if open vertical bar straight a with rightwards arrow on top close vertical bar squared plus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space 1
    i.e if left parenthesis 1 right parenthesis squared plus space cos space straight theta space plus space cos space straight theta space plus space 1 space equals space 1 space space space space space space space space space space space space space space space open square brackets because space space of space left parenthesis 1 right parenthesis comma space space left parenthesis 2 right parenthesis close square brackets
    i.e. if     2 space cos space straight theta space equals space minus 1
    i.e.  if     cos space straight theta space equals space minus 1 half
    i.e.  if    straight theta space equals space fraction numerator 2 space straight pi over denominator 3 end fraction                            open square brackets because space minus 1 half space equals negative cos space 60 degree space equals space cos space left parenthesis 180 degree minus 60 degree right parenthesis space equals space cos space 120 degree space equals space cos space fraction numerator 2 space straight pi over denominator 3 end fraction close square brackets
    therefore space space space left parenthesis straight D right parenthesis space is space correct space answer.

    Question 465
    CBSEENMA12034142

    Using vectors, prove Cosine formula 
    cos space straight C space equals space fraction numerator straight a squared plus straight b squared minus straight c squared over denominator 2 ab end fraction

    Solution

    Let BC with rightwards arrow on top space equals space straight a with rightwards arrow on top,  CA with rightwards arrow on top space equals straight b with rightwards arrow on top comma space AB with rightwards arrow on top space equals straight c with rightwards arrow on top
    therefore space space space BC space equals space straight a comma space space space CA space equals space straight b comma space space space AB space equals space straight c
    Now, straight a with rightwards arrow on top plus straight b with rightwards arrow on top equals negative straight c with rightwards arrow on top
    rightwards double arrow space space space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis squared space equals space left parenthesis negative straight c with rightwards arrow on top right parenthesis squared
rightwards double arrow space space space space straight a with rightwards arrow on top squared plus straight b with rightwards arrow on top squared space plus space 2 space straight a with rightwards arrow on top space straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top squared
rightwards double arrow space space straight a squared plus straight b squared plus 2 space ab space cos left parenthesis 180 degree space minus space straight C right parenthesis space equals space straight c squared
rightwards double arrow space space space straight a squared plus straight b squared minus 2 space ab space cos space straight C space equals space straight c squared
rightwards double arrow space space straight a squared plus straight b squared minus 2 space ab space cos space straight C space equals straight c squared space space space space space space space space space space rightwards double arrow space space space space 2 space ab space cos space straight C space equals space straight a squared plus straight b squared minus straight c squared
rightwards double arrow space space cos space straight C space equals space fraction numerator straight a squared plus straight b squared minus straight c squared over denominator 2 space straight a space straight b end fraction

    Question 466
    CBSEENMA12034143

    Using vectors, prove cosine formula 
    (i) cos space straight A space equals space fraction numerator straight b squared plus straight c squared minus straight a squared over denominator 2 space straight b space straight c end fraction

    (ii) cos space straight B space equals fraction numerator straight c squared plus straight a squared minus straight b squared over denominator 2 ca end fraction

    Solution

    (i) Let BC with rightwards arrow on top space equals straight a with rightwards arrow on top. space space CA with rightwards arrow on top space equals straight b with rightwards arrow on top comma space AB with rightwards arrow on top space equals space straight c with rightwards arrow on top
     therefore space space space space BC space equals space straight a comma space space space CA space equals space straight b comma space space AB space equals space straight c
    Now,    straight b with rightwards arrow on top plus straight c with rightwards arrow on top space equals space minus straight a with rightwards arrow on top
    rightwards double arrow space space left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis squared space equals space left parenthesis negative straight a with rightwards arrow on top right parenthesis squared
rightwards double arrow space space space straight b with rightwards arrow on top squared plus straight c with rightwards arrow on top squared space plus space 2 space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space equals space straight a with rightwards arrow on top squared
rightwards double arrow space space straight b squared plus straight c squared space plus space 2 space straight b space straight c space cos space left parenthesis 180 degree space minus space straight A right parenthesis space equals space straight a squared
rightwards double arrow space space straight b squared plus straight c squared space minus 2 space straight b space straight c space cos space straight A space equals space straight a squared space space space space space rightwards double arrow space space space 2 space straight b space straight c space cos space straight A space equals space straight b squared plus straight c squared minus straight a squared
therefore space space space space cos space straight A space equals fraction numerator straight b squared plus straight c squared minus straight a squared over denominator 2 bc end fraction

    (ii)    Now straight c with rightwards arrow on top plus straight a with rightwards arrow on top space equals space minus straight b with rightwards arrow on top            rightwards double arrow space space space left parenthesis straight c with rightwards arrow on top plus straight a with rightwards arrow on top right parenthesis squared space equals space left parenthesis negative straight b with rightwards arrow on top right parenthesis squared
    rightwards double arrow space space space space straight c with rightwards arrow on top squared plus straight a with rightwards arrow on top squared space plus space 2 space straight c with rightwards arrow on top. space straight a with rightwards arrow on top space equals space straight b with rightwards arrow on top squared space space space space space space space space rightwards double arrow space space straight c squared plus straight a squared plus 2 space straight c space straight a space left parenthesis 180 degree minus straight B right parenthesis space equals straight b squared
rightwards double arrow space space space space straight c squared plus straight a squared minus 2 space straight c space straight a space cos space straight B space equals space straight b squared space space space space space space rightwards double arrow space space space 2 space straight c space straight a space cos space straight B space equals straight c squared plus straight a squared minus straight b squared
therefore space space space cos space straight B space equals space fraction numerator straight c squared plus straight a squared minus straight b squared over denominator 2 ca end fraction.

    Question 467
    CBSEENMA12034144

    In any triangle ABC, prove the Projection Formula
    a = b cos C + c cos B.  

    Solution

    Let BC with rightwards arrow on top space equals space straight a with rightwards arrow on top comma space space CA with rightwards arrow on top space equals straight b with rightwards arrow on top comma space AB with rightwards arrow on top space equals straight c with rightwards arrow on top so that BC = a,  CA = b,   AB = c
    Now,   straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top 
    therefore space space straight a with rightwards arrow on top space. space left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space equals space 0
therefore space space straight a with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top. space straight c with rightwards arrow on top space equals space 0
therefore space space space straight a squared plus ab space cos space left parenthesis 180 degree minus straight C right parenthesis space plus space straight a space straight c space cos space straight theta space left parenthesis 180 degree minus straight B right parenthesis space equals 0
therefore space space straight a squared minus space ab space cos space straight C space minus space straight a space straight c space cosB space equals space 0
therefore space space straight a minus straight b space cos space straight C space minus space straight c space cos space straight B space equals space 0
therefore space space space straight a space equals space space straight b space cos space straight C space plus space straight c space cos space straight B.

    Question 468
    CBSEENMA12034146

    Prove that in any triangle ABC, c = a cos B + b cos A.

    Solution

    Let BC with rightwards arrow on top space equals straight a comma space space CA with rightwards arrow on top space equals space straight b with rightwards arrow on top
       AB with rightwards arrow on top space equals straight c with rightwards arrow on top space so space that
BC space equals space straight a comma space space space CA space equals space straight b comma space space AB space equals space straight c
    Now,   straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top
    rightwards double arrow space space straight c with rightwards arrow on top. space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space equals space 0
rightwards double arrow space space straight c with rightwards arrow on top. space straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top. space straight c with rightwards arrow on top space equals space 0
space space space space space space space space straight c space straight a space cos space left parenthesis 180 degree minus straight A right parenthesis space plus space straight c space straight b space cos space left parenthesis 180 degree space minus space straight B right parenthesis space plus space straight c squared space equals space 0
rightwards double arrow space space space minus straight c space straight a space cos space straight B space minus space straight c space straight b space cos space straight A space plus straight c squared space equals space 0
rightwards double arrow space space space space minus space straight a space cos space straight B space minus space straight b space cos space straight A space equals space minus straight c
therefore space space space space space space space straight c space equals space straight a space cos space straight B space plus space straight b space cos space straight A

    Question 469
    CBSEENMA12034147

    Prove that an angle inscribed in a semi-circle is a right angle.

    Solution
    Let O be the centre of the semi circle and AB be the diameter. Let P be any point on the circumference of the semi circle.
    Let OA with rightwards arrow on top space equals space straight a with rightwards arrow on top comma space space then space OB with rightwards arrow on top space equals negative straight a with rightwards arrow on top.
    Let OP with rightwards arrow on top space equals space straight r with rightwards arrow on top
    therefore space space space AP with rightwards arrow on top space equals OP with rightwards arrow on top space minus space OA with rightwards arrow on top space equals space straight r with rightwards arrow on top space minus space straight a with rightwards arrow on top
space space space space space space space BP with rightwards arrow on top space equals space OP with rightwards arrow on top space minus space OB with rightwards arrow on top space equals straight r with rightwards arrow on top space minus space left parenthesis straight a with rightwards arrow on top right parenthesis space equals space straight r with rightwards arrow on top plus straight a with rightwards arrow on top
AP with rightwards arrow on top space BP with rightwards arrow on top space equals space left parenthesis straight r with rightwards arrow on top space minus space straight a with rightwards arrow on top right parenthesis. space left parenthesis straight r with rightwards arrow on top space plus space straight a with rightwards arrow on top right parenthesis space equals space straight r with rightwards arrow on top squared space minus space straight a with rightwards arrow on top squared
space space space space space space space space space space space space space equals straight a squared minus straight a squared space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because straight r space equals space straight a space as space OP space equals space OA close square brackets
therefore space space space AP with rightwards arrow on top space space is space perpendicular space to space BP with rightwards arrow on top
rightwards double arrow space space angle APB space space equals space 90 degree
Hence space the space result. space space space space space space space space

    Question 470
    CBSEENMA12034148

    Using vectors, prove that if two medians of a triangle ABC be equal, then it is an isosceles triangle. 

    Solution
    Let BE and CF be two medians of ∆ABC.
    Take A an origin. Let AB with rightwards arrow on top space equals straight b with rightwards arrow on top comma space space AC with rightwards arrow on top space equals space straight c with rightwards arrow on top
    Since E is mid-point of AC
    therefore space space space space position vector of E is 1 half straight c with rightwards arrow on top
    Similarly position vector of F is 1 half straight b with rightwards arrow on top.
    Now,  BE with rightwards arrow on top space equals space AE with rightwards arrow on top space minus space AB with rightwards arrow on top space equals space 1 half straight c with rightwards arrow on top minus straight b with rightwards arrow on top
    and    CF with rightwards arrow on top space equals AF with rightwards arrow on top space minus space AC with rightwards arrow on top space equals 1 half straight b with rightwards arrow on top minus straight c with rightwards arrow on top

    From given condition, 
                          BE space equals space CF space or space BE squared space equals space CF squared
    therefore space space space space space open parentheses space BE with rightwards arrow on top close parentheses squared space equals space open parentheses CF with rightwards arrow on top close parentheses squared
rightwards double arrow space space space space space space space space space space space space space space space space open parentheses 1 half straight c with rightwards arrow on top minus straight b with rightwards arrow on top close parentheses squared space equals space open parentheses 1 half straight b with rightwards arrow on top minus straight c with rightwards arrow on top close parentheses squared
rightwards double arrow space space space space 1 fourth straight c with rightwards arrow on top squared space plus space straight b with rightwards arrow on top squared space minus space straight c with rightwards arrow on top. straight b with rightwards arrow on top space equals space 1 fourth straight b with rightwards arrow on top squared space plus space straight c with rightwards arrow on top squared space minus space straight b with rightwards arrow on top. space straight c with rightwards arrow on top
rightwards double arrow space space space space space space space space space space space 1 fourth straight c squared plus straight b squared space equals space 1 fourth straight b squared plus straight c squared space space space space rightwards double arrow space space space space 3 over 4 straight b squared space equals space 3 over 4 straight c squared
rightwards double arrow space space space space space space space straight b squared space equals space straight c squared space space space rightwards double arrow space space space space straight b space equals space straight c space space space rightwards double arrow space space space AB space space equals space AC
because space space space space space increment ABC space is space isosceles.
    Question 471
    CBSEENMA12034149

    Using vectors, prove that the perpendicular bisectors of the sides of a triangle are concurrent.

    Solution

    Let ABC be the given triangle and O be the point of intersection of perpendicular bisectors OD and OE of sides BC and CA respectively.
    Let F be mid-point of AB. Join O to F.
    Take O as origin.

    Let straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top be the position vectors of A, B, C respectively.
                therefore space space OA space equals space straight a with rightwards arrow on top comma space space OB with rightwards arrow on top space equals space straight b with rightwards arrow on top comma space space OC with rightwards arrow on top space equals straight c with rightwards arrow on top
    The position vectors of D, E, F are fraction numerator straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction comma space space fraction numerator straight c with rightwards arrow on top plus straight a with rightwards arrow on top over denominator 2 end fraction comma space fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top over denominator 2 end fraction respectively.
    Since               OD space perpendicular space BC
    therefore space space space space space space space OD with rightwards arrow on top. space BC with rightwards arrow on top space equals space 0
rightwards double arrow space space space space open parentheses fraction numerator straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction close parentheses. space left parenthesis straight c with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space equals space space 0 space space space space rightwards double arrow space space 1 half left parenthesis straight c with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. space left parenthesis straight c with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis space equals space 0
rightwards double arrow space space space 1 half left parenthesis straight c with rightwards arrow on top squared minus straight b with rightwards arrow on top squared right parenthesis space equals space 0
    Again, OE space perpendicular space CA
    therefore space space space OE with rightwards arrow on top. space CA with rightwards arrow on top space equals space 0 space space space space rightwards double arrow space space space open parentheses fraction numerator straight c with rightwards arrow on top plus straight a with rightwards arrow on top over denominator 2 end fraction close parentheses. space left parenthesis straight a with rightwards arrow on top. space straight c with rightwards arrow on top right parenthesis space equals space 0
rightwards double arrow space space space 1 half left parenthesis straight a with rightwards arrow on top squared minus straight c with rightwards arrow on top squared right parenthesis space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis
    Adding (1) and (2), we get,
                  1 half left parenthesis straight a with rightwards arrow on top space minus straight b with rightwards arrow on top squared right parenthesis space space space space rightwards double arrow space space space 1 half left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. space space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space equals space 0
    rightwards double arrow space space space open parentheses fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top over denominator 2 end fraction close parentheses space. space left parenthesis straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top right parenthesis space equals space stack OF. with rightwards arrow on top space AB with rightwards arrow on top space equals space 0
rightwards double arrow space space space space OF space perpendicular space AB
    therefore    perpendicular bisectors meet in a point. 

    Question 472
    CBSEENMA12034150

    Prove that the median to the base of isosceles triangle is perpendicular to the base.

    Solution
    Let ABC be an isosceles triangle with AB = AC and let AD be the median to the base BC. Then D is the middle point of BC.

    Take A as origin. Let straight b with rightwards arrow on top comma space straight c with rightwards arrow on top be position vectors of B and C respectively with respect to origin A such that AB with rightwards arrow on top space equals space straight b with rightwards arrow on top comma space space AC with rightwards arrow on top space equals straight c with rightwards arrow on top.  Then position vector of D w.r.t A is fraction numerator straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction.
    Now,    BC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight B space equals straight c with rightwards arrow on top minus straight b with rightwards arrow on top
    therefore space space space BC with rightwards arrow on top. space AD with rightwards arrow on top space equals space left parenthesis straight c with rightwards arrow on top space minus straight b with rightwards arrow on top right parenthesis. space open parentheses fraction numerator straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction close parentheses space equals space 1 half left parenthesis straight c with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space left parenthesis straight c with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis
space space space space space space space space space space space space space space space space space space space space space space equals space 1 half left parenthesis straight c with rightwards arrow on top squared space minus space straight b with rightwards arrow on top squared right parenthesis space equals space 1 half left parenthesis open vertical bar straight c with rightwards arrow on top close vertical bar squared space minus space open vertical bar straight b with rightwards arrow on top close vertical bar squared right parenthesis
space space space space space space space space space space space space space space space space space space space space space space space equals space 1 half left parenthesis AC squared minus space AB squared right parenthesis space equals space 1 half left parenthesis 0 right parenthesis space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because AC space equals space AB close square brackets
therefore space space space BC with rightwards arrow on top space is space perpendicular space to space AD with rightwards arrow on top.
Hence space the space result.
    Question 473
    CBSEENMA12034152

    If the median of the base of a triangle is perpendicular on the base, then prove that the triangle is an isosceles.

    Solution
    Let ABC be a triangle in which the median AD is perpendicular to base BC.
    Take A as origin. Let straight b with rightwards arrow on top. space straight c with rightwards arrow on top be position vectors of B and C so that AB with rightwards arrow on top space space equals space straight b with rightwards arrow on top comma space space AC with rightwards arrow on top space equals space straight c with rightwards arrow on top.
    Since D is mid-point of BC

    therefore space space space space space  position vector of D is fraction numerator straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction
    i.e.,     AD with rightwards arrow on top space equals space fraction numerator straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction
    Also,     BC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight B space equals space straight c with rightwards arrow on top minus straight b with rightwards arrow on top
    Since   AD perpendicular BC
    therefore space space space AD with rightwards arrow on top. space BC with rightwards arrow on top space equals space 0
therefore space space space space open parentheses fraction numerator straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction close parentheses. space space left parenthesis straight c with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis space equals space 0 space space space space space space rightwards double arrow space space space space space left parenthesis straight c with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. space left parenthesis straight c with rightwards arrow on top space minus straight b with rightwards arrow on top right parenthesis space space equals space 0
rightwards double arrow space space straight c with rightwards arrow on top squared space minus space straight b with rightwards arrow on top squared space equals space 0 space space space space space space space rightwards double arrow space space space space straight c with rightwards arrow on top squared space space equals space straight b with rightwards arrow on top squared space space space rightwards double arrow space space space space open vertical bar straight c with rightwards arrow on top close vertical bar squared space equals space open vertical bar straight b with rightwards arrow on top close vertical bar squared
rightwards double arrow space space space AC squared space equals space AB squared space space space space space space space space space space rightwards double arrow space space space AB space equals space AC
therefore space space space increment ABC space is space an space isosceles space triangle.
    Question 474
    CBSEENMA12034153

    (i) Prove that cos (α + β) )= cos α cos β – sin α sin β.
    (ii)  Prove that cos (α – p) = cos α cos β + sin α sin β.

    Solution

     (i) Draw a circle with centre at O and radius = 1.
    Let P, Q be two points on the circle such that
    ∠POX = α and ∠QQX = β.
    ∴  ∠POQ = α + β
    Co-ordinates of P, Q are (cos α, sin α) and (cos β, – sin β) respectively.
    (ii)  Draw a circle with centre at O and radius = 1.
    Let P, Q be two points on the circle such that
    ∠POX = α, ∠QOX = β
    ∴ ∠POQ = α – β
    Co-ordinates of P, Q are (cos α, sin α) and (cos β, sin β) respectively.

    therefore space space space space space space OP with rightwards arrow on top space equals space left parenthesis cos space straight alpha right parenthesis space straight i with hat on top space plus space left parenthesis sin space straight alpha right parenthesis space straight j with hat on top
and space space space space OQ with rightwards arrow on top space equals space left parenthesis cos space straight beta right parenthesis straight i with hat on top space plus space left parenthesis sin space straight beta right parenthesis space straight j with hat on top
Now space angle POQ space equals straight alpha minus straight beta
rightwards double arrow space space space space cos space left parenthesis straight alpha minus straight beta right parenthesis space equals space fraction numerator OP with rightwards arrow on top. space OQ with rightwards arrow on top over denominator open vertical bar OP with rightwards arrow on top close vertical bar space open vertical bar OQ with rightwards arrow on top close vertical bar end fraction space equals fraction numerator cos space straight alpha space cos space straight beta space plus space sin space straight alpha space sin space straight beta over denominator left parenthesis 1 right parenthesis thin space left parenthesis 1 right parenthesis end fraction
therefore space space space cos space left parenthesis straight alpha minus straight beta right parenthesis space equals space cos space straight alpha space cos space straight beta space plus space sin space straight alpha space sin space straight beta

    Question 475
    CBSEENMA12034155

    Prove that the diagonals of a rectangle are perpendicular if and only if the rectangle is a square.

    Solution
    Let ABCD be the given rectangle.
    Take A as origin.

    Let AB with rightwards arrow on top space equals space straight b with rightwards arrow on top comma space space space AD with rightwards arrow on top space equals space straight d.
    Now, AC with rightwards arrow on top space equals space AB with rightwards arrow on top space plus space BC with rightwards arrow on top space equals space AB with rightwards arrow on top space plus space AD with rightwards arrow on top space equals space straight b with rightwards arrow on top space plus space straight d with rightwards arrow on top
    Also,  BD with rightwards arrow on top space equals space straight P. straight V. space of space straight D space minus space straight P. straight V. space of space straight B space equals space straight d with rightwards arrow on top space minus space straight b with rightwards arrow on top.
    Now diagonals AC and BD are perpendicular if AC with rightwards arrow on top is perpendicular to BD with rightwards arrow on top.
    i.e.  iff    AC with rightwards arrow on top. space BD with rightwards arrow on top space equals space 0
    i.e. iff    left parenthesis straight b with rightwards arrow on top plus straight d with rightwards arrow on top right parenthesis. space left parenthesis straight d with rightwards arrow on top space minus straight b with rightwards arrow on top right parenthesis space equals space 0
    i.e. iff left parenthesis straight d with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis. space left parenthesis straight d with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space equals space 0
    i.e. iff  straight d with rightwards arrow on top squared space minus space straight b with rightwards arrow on top squared space equals space 0
    i.e. iff   open vertical bar straight d with rightwards arrow on top close vertical bar squared space equals space open vertical bar straight b with rightwards arrow on top close vertical bar squared
    i.e. iff AD squared space equals space AB squared
    i.e. iff AD = AB
    i.e. iff    rectangle ABCD is a square.
    Hence the result. 

    Question 476
    CBSEENMA12034156

    Using vectors, prove that a parallelogram whose diagonals are equal is a rectangle. 

    Solution
    Let OACB be a parallelogram such that OC = AB

    Let OA with rightwards arrow on top space equals space straight a with rightwards arrow on top comma space space OB with rightwards arrow on top space equals space straight b with rightwards arrow on top
    Now,  OC = AB
    rightwards double arrow space space space OC squared space equals space AB squared
rightwards double arrow space space open parentheses OA with rightwards arrow on top plus AC with rightwards arrow on top close parentheses squared space equals open parentheses AO with rightwards arrow on top space plus OB with rightwards arrow on top close parentheses squared
rightwards double arrow space space space open parentheses OA with rightwards arrow on top space plus space OB with rightwards arrow on top close parentheses squared space equals space open parentheses negative OA with rightwards arrow on top space plus space OB with rightwards arrow on top close parentheses squared
rightwards double arrow space space left parenthesis straight a with rightwards arrow on top space plus straight b with rightwards arrow on top right parenthesis squared space equals space left parenthesis negative straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis squared
rightwards double arrow space space straight a with rightwards arrow on top squared plus space straight b with rightwards arrow on top squared space plus space 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space straight a with rightwards arrow on top squared space plus space straight b with rightwards arrow on top squared space minus space 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top
rightwards double arrow space space 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space minus 2 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space space space rightwards double arrow space space space 4 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0
rightwards double arrow space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0 with rightwards arrow on top
rightwards double arrow space space space straight a with rightwards arrow on top space and space straight b with rightwards arrow on top space are space perpendicular. space space space space space space rightwards double arrow space space space angle AOB space equals space 90 degree
rightwards double arrow space space space OACB space is space straight a space rectangle.
               
    Question 477
    CBSEENMA12034157

    Prove using vectors: The quadrilateral obtained by joining mid-points of adjacent sides of a rectangle is a rhombus.

    Solution

    Let ABCD be given rectangle and P, Q. R, S be mid-points of sides AB, BC, CD, DA respectively.
    Take A as origin.

      Let   AB with rightwards arrow on top space equals space straight b with rightwards arrow on top comma space space space AD with rightwards arrow on top space equals space straight c with rightwards arrow on top comma space space AD with rightwards arrow on top space equals space straight d with rightwards arrow on top
    therefore space space space space space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top comma space straight d with rightwards arrow on top space are space position space vectors space of space straight B comma space straight C comma space straight D space referred space to space straight A space as space origin.
               The position vectors of P, Q, R, S are fraction numerator straight b with rightwards arrow on top over denominator 2 end fraction comma space fraction numerator straight b with rightwards arrow on top plus straight c with rightwards harpoon with barb upwards on top over denominator 2 end fraction comma space fraction numerator straight c with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction comma space fraction numerator straight d with rightwards arrow on top over denominator 2 end fraction space respectively.
       therefore space space space space space PR with rightwards arrow on top space equals space straight P. straight V. space of space straight R space minus space straight P. straight V. space of space straight P space equals space fraction numerator straight c with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction minus fraction numerator straight b with rightwards arrow on top over denominator 2 end fraction
space space space space space space space space space space space space space space space space equals space 1 half left parenthesis straight c with rightwards arrow on top plus straight d with rightwards arrow on top space minus straight b with rightwards arrow on top right parenthesis space equals space 1 half open curly brackets left parenthesis straight d with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis space plus space straight c with rightwards arrow on top close curly brackets
therefore space space space space QS with rightwards arrow on top space equals space straight P. straight V. space of space straight S space minus space straight P. straight V. space of space straight Q space equals space fraction numerator straight d with rightwards arrow on top over denominator 2 end fraction space minus fraction numerator straight b with rightwards arrow on top plus straight c with rightwards arrow on top over denominator 2 end fraction
space space space space space space space space space space space space space space space space equals space 1 half left parenthesis straight d with rightwards arrow on top minus straight b with rightwards arrow on top minus straight c with rightwards arrow on top right parenthesis space equals space 1 half open curly brackets left parenthesis straight d with rightwards arrow on top space minus straight b with rightwards arrow on top right parenthesis space minus space straight c with rightwards arrow on top close curly brackets
    therefore space space space space PR with rightwards arrow on top. space QS with rightwards arrow on top space equals space 1 fourth left curly bracket left parenthesis straight d with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space plus space straight c with rightwards arrow on top right curly bracket. space left curly bracket left parenthesis straight d with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space minus space straight c with rightwards arrow on top right curly bracket space equals space 1 fourth left curly bracket left parenthesis straight d with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis squared space minus space straight c with rightwards arrow on top squared right curly bracket
                         equals space 1 fourth left curly bracket straight d with rightwards arrow on top squared plus straight b with rightwards arrow on top squared space minus space 2 space straight d with rightwards arrow on top. space straight b with rightwards arrow on top space minus space straight c with rightwards arrow on top squared right curly bracket
equals space 1 fourth left curly bracket straight d with rightwards arrow on top squared space plus space straight b with rightwards arrow on top squared space minus space 2 space straight d with rightwards arrow on top. space straight b with rightwards arrow on top space minus space straight c with rightwards arrow on top squared right curly bracket
equals space 1 fourth left parenthesis straight b with rightwards arrow on top squared plus space straight d with rightwards arrow on top squared space minus space straight c with rightwards arrow on top squared right parenthesis space space space space space space space space space open square brackets because space space straight b with rightwards arrow on top. space straight d with rightwards arrow on top space equals space 0 space as space ABCD space is space straight a space rectangle close square brackets
equals space 1 fourth open square brackets open vertical bar straight b with rightwards arrow on top close vertical bar squared space plus space open vertical bar straight d with rightwards arrow on top close vertical bar squared space minus space open vertical bar straight c with rightwards arrow on top close vertical bar squared close square brackets space equals space 1 fourth left parenthesis AB squared plus AD squared minus AC squared right parenthesis
equals space 1 fourth left parenthesis AB squared plus BC squared minus AC squared right parenthesis space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets therefore AD space equals space BC close square brackets
equals space 1 fourth left parenthesis AC squared minus AC squared right parenthesis space equals 1 fourth left parenthesis 0 right parenthesis
space equals space 0
    therefore space space space PR thin space perpendicular space QS
    rightwards double arrow   PQRS is a rhombus.
     

    Question 478
    CBSEENMA12034160

    Show that the angle between two diagonals of a cube is cos to the power of negative 1 end exponent space open parentheses 1 third close parentheses.

    Solution
    Take O, a comer of cube OBLCMANP, as origin and OA, OB, OC. the three edges through it as the axes.

    Let OA = OB = OC = α, then the co-ordinates of O, A, B, C are (0, 0, 0),
    (a, 0. 0), (0, a, 0). (0, 0, a) respectively ; those of P, L, M, N are (a, a, a),(0, a. a), (a, 0, a), (a, a, 0) respectively.
    The four diagonals are
    OP, AL, BM, CN.
    Consider the diagonals AL and BM
    AL with rightwards arrow on top space equals space straight P. straight V. space of space straight L space minus space straight P. straight V. space of space straight A space equals space left parenthesis straight a space straight j with hat on top space plus space straight a space straight k with hat on top right parenthesis space minus space left parenthesis straight a space straight i with hat on top right parenthesis space equals space minus straight a space straight i with hat on top space plus straight a space straight j with hat on top space plus space straight a space straight k with hat on top
    BM with rightwards arrow on top space equals space straight P. straight V. space of space straight M space minus space straight P. straight V. space of space straight B space equals space left parenthesis straight a straight i with hat on top space plus space straight a space straight k with hat on top right parenthesis space minus space left parenthesis straight a space straight j with hat on top right parenthesis space equals space straight a space straight i with hat on top space minus space straight a space straight j with hat on top space plus space straight a space straight k with hat on top
    Let  straight theta be angle between AL and BM.
    therefore space space space cos space straight theta space equals space fraction numerator AL with rightwards arrow on top space BM with rightwards arrow on top over denominator open vertical bar AL with rightwards arrow on top close vertical bar space open vertical bar BM with rightwards arrow on top close vertical bar end fraction space equals space fraction numerator left parenthesis negative straight a right parenthesis thin space left parenthesis straight a right parenthesis space plus space left parenthesis straight a right parenthesis thin space left parenthesis negative straight a right parenthesis space plus space left parenthesis straight a right parenthesis space left parenthesis straight a right parenthesis over denominator square root of straight a squared plus straight a squared plus straight a squared end root space square root of straight a squared plus straight a squared plus straight a squared end root end fraction
space space space space space space space space space space space space space space space space space equals space fraction numerator negative straight a squared minus straight a squared plus straight a squared over denominator square root of 3 space straight a squared end root space square root of 3 straight a squared end root end fraction space equals space minus fraction numerator straight a squared over denominator 3 straight a squared end fraction space equals space minus 1 third
    therefore space space space acute space angle space straight theta space is space given space by
                                  cos space straight theta space equals space 1 third
    therefore space space space straight theta space equals space cos to the power of negative 1 end exponent space open parentheses 1 third close parentheses
    Similarly the angle between the other pairs of diagonals is cos to the power of negative 1 end exponent open parentheses 1 third close parentheses.
    Question 479
    CBSEENMA12034161

    Prove, using vectors, that the altitudes of a triangle are concurrent.
    OR
    Prove that the perpendicular from the vertices to the opposite sides of a triangle are concurrent. 

    Solution

    Let ABC be given triangle and H be the point of intersection of altitudes AL and BM. Join CH and produce it to meet BA in N.
    Take H as origin.

       Let straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space stack straight c with rightwards arrow on top with rightwards arrow on top be the position vectors of A, B, C respectively.
    therefore space space space space space HA with rightwards arrow on top space equals space straight a with rightwards arrow on top comma space space HB with rightwards arrow on top space equals space straight b with rightwards arrow on top comma space space HC with rightwards arrow on top space equals space straight c with rightwards arrow on top.
    Since AL space perpendicular space BC
      therefore space space space space AH with rightwards arrow on top. space space BC with rightwards arrow on top space equals space 0
therefore space space space space minus straight a with rightwards arrow on top. space space left parenthesis straight c with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space equals space 0
therefore space space space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top. space space straight c with rightwards arrow on top space space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
    Again,  BM perpendicular CA
    therefore space space space space BH with rightwards arrow on top space. space CA with rightwards arrow on top space equals space 0
rightwards double arrow space space minus space stack straight b. with rightwards arrow on top space left parenthesis straight a with rightwards arrow on top space minus space straight c with rightwards arrow on top right parenthesis space equals space space 0 space space space space space space rightwards double arrow space space space space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space minus space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space equals space 0
    rightwards double arrow space space space space space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space minus space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0                                                   ...(2)
    Adding (1) and (2), we get,
                straight b with rightwards arrow on top. space straight c with rightwards arrow on top space minus space straight a with rightwards arrow on top. space straight c with rightwards arrow on top space equals space space 0 space space space space space space space space rightwards double arrow space space space space left parenthesis straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top right parenthesis. space straight c with rightwards arrow on top space equals space 0
    rightwards double arrow space space minus space straight c with rightwards arrow on top. space thin space left parenthesis straight a with rightwards arrow on top space minus space stack straight b right parenthesis with rightwards arrow on top space equals space 0 space space space space rightwards double arrow space space space space CH with rightwards arrow on top. space space BA with rightwards arrow on top space equals space 0
rightwards double arrow space space space space space space CH space perpendicular space AB space space space space space space space space space space space space space space space space space rightwards double arrow space space space space CN thin space perpendicular space AB
therefore space space space space space space space space space space altitudes space of space increment ABC space meet space in space straight a space point space straight H.

    Question 480
    CBSEENMA12034162

    Show that the diagonals of a rhombus bisect each other at right angles.

    Solution
    Let ABCD be the rhombus. Take A as origin.

        Let straight b with rightwards arrow on top comma space straight d with rightwards arrow on top be the position vectors of B and D respectively so that
                               AB with rightwards arrow on top space equals space straight b with rightwards arrow on top comma space space AD with rightwards arrow on top space equals space straight d with rightwards arrow on top
    Now,        AC with rightwards arrow on top space equals space AB with rightwards arrow on top space space plus space BC with rightwards arrow on top space equals space AB with rightwards arrow on top space plus space AD with rightwards arrow on top
                                                                   [because BC is equal and parallel to AD]
    therefore space space space AC with rightwards arrow on top space equals space straight b with rightwards arrow on top space plus space straight d with rightwards arrow on top
    Position vector of mid-point of diagonal AC is fraction numerator 0 with rightwards arrow on top plus left parenthesis straight b with rightwards arrow on top plus straight d with rightwards arrow on top right parenthesis over denominator 2 end fraction space space or space space fraction numerator straight b with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction
    Also position vector of mid-point of diagonal BD is fraction numerator straight b with rightwards arrow on top plus straight d with rightwards arrow on top over denominator 2 end fraction

    ∴    position vector of mid-point of diagonal AC is same as position vector of mid-point of diagonals BD.
    ∴  diagonals AC and BD bisect each other.
    Also,  AC with rightwards arrow on top. space BD with rightwards arrow on top space equals space left parenthesis straight b with rightwards arrow on top plus straight d with rightwards arrow on top right parenthesis. space left parenthesis straight d with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis
                                              open square brackets because space space BD with rightwards arrow on top space equals space straight P. straight V. space of space straight D space minus space straight P. straight V. space of space straight B space equals space straight d with rightwards arrow on top minus straight b with rightwards arrow on top close square brackets
    equals space straight d with rightwards arrow on top squared space minus space straight b with rightwards arrow on top squared space equals space AD squared space minus space AB squared
equals space space 0
                                               [because AD = AB as all sides of rhombus are equal]
    therefore space space space AC with rightwards arrow on top space is space perpendicular space to space BD with rightwards arrow on top.
    therefore diagonals AC and BD are perpendicular to each other. 
    Hence the result. 

    Question 481
    CBSEENMA12034163

    In a triangle OAB , ∠AOB = 90°. If P and Q are the points of trisection of AB, prove that OP squared space plus space OQ squared space equals space 5 over 9 AB squared

    Solution

    Take O as origin,  OA with rightwards arrow on top space equals straight a with rightwards arrow on top comma space space OB with rightwards arrow on top space equals space straight b with rightwards arrow on top
    because space space space angle AOB space equals space 90 degree space space space space space space space space space space space space because space space OA with rightwards arrow on top. space OB with rightwards arrow on top space equals space 0 space space space space space space space space space space space rightwards double arrow space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0
    Let P divide AB in the ratio 1 : 2
    because space straight P. straight V. space of space straight P space equals space fraction numerator 2 straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top over denominator 3 end fraction
    Let Q divide AB in the ratio 2 : 1
    because space straight P. straight V. space of space straight Q space equals space fraction numerator straight a with rightwards arrow on top space plus space 2 space straight b with rightwards arrow on top over denominator 3 end fraction
    L.H.S. = OP squared plus OQ squared space equals space open parentheses fraction numerator 2 space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top over denominator 3 end fraction close parentheses squared space plus space open parentheses fraction numerator straight a with rightwards arrow on top space plus 2 space straight b with rightwards arrow on top over denominator 3 end fraction close parentheses space equals space 1 over 9 open square brackets left parenthesis 2 space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis space squared space plus space left parenthesis straight a with rightwards arrow on top space plus space 2 space straight b with rightwards arrow on top right parenthesis squared close square brackets
                equals space 1 over 9 open square brackets 4 straight a with rightwards arrow on top squared space plus space straight b with rightwards arrow on top squared space plus space 4 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top squared space plus space 4 space straight b with rightwards arrow on top squared space minus space 4 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top close square brackets
equals space 1 over 9 left parenthesis 5 straight a with rightwards arrow on top squared space plus space 5 straight b with rightwards arrow on top squared right parenthesis space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
space equals 5 over 9 left parenthesis straight a with rightwards arrow on top squared plus space straight b with rightwards arrow on top squared right parenthesis

    R.H.S. = 5 over 9 AB squared space equals space 5 over 9 AB with rightwards arrow on top squared space equals space 5 over 9 left parenthesis straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A right parenthesis squared
               equals space 5 over 9 left parenthesis straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top right parenthesis squared space equals space 5 over 9 left square bracket straight b with rightwards arrow on top squared space plus space straight a with rightwards arrow on top squared space minus space space 2 space straight b with rightwards arrow on top. space straight a with rightwards arrow on top right square bracket space equals space 5 over 2 left parenthesis straight a with rightwards arrow on top squared space plus space straight b with rightwards arrow on top squared right parenthesis space space space space left square bracket because space of space left parenthesis 1 right parenthesis right square bracket
because space space space space straight L. straight H. straight S. space equals space straight R. straight H. straight S.

    Question 482
    CBSEENMA12034164

    In a tetrahedron, if two pairs of opposite edges are perpendicular, then the third pair is also perpendicular to each other and the sum of the sequares of two opposite edges is the same for each pair.

    Solution
    Let ABCD be the tetrahedron. Take D as origin,
    DA with rightwards arrow on top space equals space straight a with rightwards arrow on top comma space space space DB with rightwards arrow on top space equals space straight b with rightwards arrow on top comma space space DC with rightwards arrow on top space equals space straight c with rightwards arrow on top space so space that space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top are position vectors of A, B, C  respectively with D as origin. Let DA and CB be perpendicular.

    therefore space space DA with rightwards arrow on top. space CB with rightwards arrow on top space equals space 0 space space space or space space straight a with rightwards arrow on top. space left parenthesis straight b with rightwards arrow on top space minus space straight c with rightwards arrow on top right parenthesis space equals space 0 space space space space space... left parenthesis 1 right parenthesis
    Let DB and AC be perpendicular.
            therefore space space DB with rightwards arrow on top. space AC with rightwards arrow on top space equals space 0 comma space space space or space space straight b with rightwards arrow on top. space left parenthesis straight c with rightwards arrow on top space minus space straight a with rightwards arrow on top right parenthesis space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis
Adding space left parenthesis 1 right parenthesis space and space left parenthesis 2 right parenthesis comma space we space get space straight a with rightwards arrow on top. space left parenthesis straight b with rightwards arrow on top space minus space straight c with rightwards arrow on top right parenthesis space plus space straight b with rightwards arrow on top. space left parenthesis straight c with rightwards arrow on top space minus straight a with rightwards arrow on top right parenthesis space equals space 0
therefore space space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top. space straight c with rightwards arrow on top space plus space straight b with rightwards arrow on top space. space straight c with rightwards arrow on top space minus space straight b with rightwards arrow on top. space straight a with rightwards arrow on top space equals space 0 space space space or space space space straight c with rightwards arrow on top. space left parenthesis straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top right parenthesis space equals space 0
or space space DC with rightwards arrow on top. space AB with rightwards arrow on top space equals 0.
    or space space DC with rightwards arrow on top space. space AB with rightwards arrow on top space equals space 0.
    therefore space space space space space space space DC space is space perpendicular space to space AB.
    Again,  DA squared plus CB squared space equals space straight a with rightwards arrow on top squared space plus space left parenthesis straight b with rightwards arrow on top space minus space straight c with rightwards arrow on top right parenthesis squared space equals space straight a with rightwards arrow on top squared plus straight b with rightwards arrow on top squared space plus space straight c with rightwards arrow on top squared space minus space 2 straight b with rightwards arrow on top. straight c with rightwards arrow on top
    DB squared plus AC squared space equals straight b with rightwards arrow on top squared space plus space left parenthesis straight c with rightwards arrow on top space space minus straight a with rightwards arrow on top right parenthesis squared space equals space straight a with rightwards arrow on top squared space plus straight b with rightwards arrow on top squared space plus space straight c with rightwards arrow on top squared space minus space 2 space straight c with rightwards arrow on top space. straight a with rightwards arrow on top
DC squared plus AB squared space equals space straight c with rightwards arrow on top squared plus space left parenthesis straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top right parenthesis squared space equals straight a with rightwards arrow on top squared plus straight b with rightwards arrow on top squared space plus straight c with rightwards arrow on top squared minus space 2 straight a with rightwards arrow on top. space straight b with rightwards arrow on top
Now space from space left parenthesis 1 right parenthesis comma space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top. space equals straight a with rightwards arrow on top. space straight c with rightwards arrow on top
From space left parenthesis 2 right parenthesis comma space space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space equals space straight a with rightwards arrow on top. space straight b with rightwards arrow on top
therefore space space space we space have space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space minus straight b with rightwards arrow on top. space straight c with rightwards arrow on top space equals space straight c with rightwards arrow on top. space straight a with rightwards arrow on top
therefore space space DA squared plus CB squared space equals space DB squared plus AC squared space equals space DC squared plus AB squared
Hence space the space result.
     




    Question 483
    CBSEENMA12034165

    Find straight lambda space and space straight mu if  left parenthesis 2 space straight i with hat on top space plus space 6 space straight j with hat on top space plus space 27 space straight k with hat on top right parenthesis space cross times left parenthesis straight i with hat on top space cross times space straight lambda space straight j with hat on top space plus space straight mu space straight k with hat on top right parenthesis space equals space 0 with rightwards arrow on top.

    Solution

    Here  left parenthesis 2 space straight i with hat on top space plus space 6 space straight j with hat on top space plus space 27 space straight k with hat on top right parenthesis space cross times space left parenthesis straight i with hat on top space plus space straight lambda space straight j with hat on top space plus space straight mu space straight k with hat on top right parenthesis space equals space 0 with rightwards arrow on top
    therefore space space space space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 2 6 27 row 1 straight lambda straight mu end table close vertical bar space equals space 0 with rightwards arrow on top
therefore space space space space space straight i with hat on top space open vertical bar table row 6 27 row straight lambda straight mu end table close vertical bar space minus space straight j with hat on top space open vertical bar table row 2 27 row 1 straight mu end table close vertical bar space plus space straight k with hat on top space open vertical bar table row 2 6 row 1 straight lambda end table close vertical bar space equals 0 with rightwards arrow on top
therefore space space space space space space left parenthesis 6 space straight mu space minus space 27 space straight lambda right parenthesis straight i with hat on top space minus space left parenthesis 2 straight mu minus 27 right parenthesis space straight j with hat on top space plus left parenthesis 2 straight lambda minus 6 right parenthesis space straight k with hat on top space equals space 0 with rightwards arrow on top
rightwards double arrow space space space space space space space space space 6 space straight mu space minus 27 space straight lambda space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... space space left parenthesis 1 right parenthesis
space space space space space space space space minus left parenthesis 2 straight mu minus 27 right parenthesis space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis
and space space 2 space straight lambda minus 6 space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 3 right parenthesis
From space left parenthesis 3 right parenthesis comma space 2 space straight lambda space equals space 6 comma space space space space space space space space space space space rightwards double arrow space space straight lambda space equals space 3
From space left parenthesis 2 right parenthesis comma space 2 space straight mu space equals space 27 comma space space space space space space space space space rightwards double arrow space straight mu space equals space 27 over 2
Putting space space space space space straight lambda space equals space 3 comma space space space straight mu space equals space 27 over 2 space in space left parenthesis 1 right parenthesis comma space we space get comma
space space space space space space 6 open parentheses 27 over 2 close parentheses space minus space 27 space cross times 3 space equals space 0
or space space space 81 minus 81 space equals space 0
or space space space space space space space space space space 0 space equals space 0
therefore space space space space space space space space space space space straight lambda space equals space 3 comma space space space straight mu space equals space 27 over 2 space satisfy space all space the space equations
therefore space space space space space space space space space space space straight lambda space equals space 3 comma space space space straight mu space equals space 27 over 2

    Question 484
    CBSEENMA12034166

    Find open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar comma space space space if space space straight a with rightwards arrow on top space equals space 2 space straight i with hat on top space plus straight j with hat on top space plus space 3 straight k with hat on top space and space straight b with rightwards arrow on top space equals space 3 space straight i with hat on top space plus space 5 space straight j with hat on top space minus space 2 space straight k with hat on top.

    Solution

    Here,    straight a with rightwards arrow on top space equals space 2 straight i with hat on top space plus space straight j with hat on top space plus space 3 straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space 3 space straight i with hat on top space plus space 5 space straight j with hat on top space minus space 2 space straight k with hat on top
    therefore space space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 2 1 3 row 3 5 cell negative 2 end cell end table close vertical bar space equals space straight i with hat on top space open vertical bar table row 1 3 row 5 cell negative 2 end cell end table close vertical bar space minus space straight j with hat on top space open vertical bar table row 2 3 row 3 cell negative 2 end cell end table close vertical bar plus space straight k with hat on top space open vertical bar table row 2 1 row 3 5 end table close vertical bar
                         equals space left parenthesis negative 2 minus 15 right parenthesis space straight i with hat on top space minus space left parenthesis negative 4 minus 9 right parenthesis space straight j with hat on top space plus space left parenthesis 10 minus 3 right parenthesis straight k with hat on top space equals space minus 17 straight i with hat on top space plus space 13 space straight j with hat on top space plus space 7 space straight k with hat on top
    therefore space space space open vertical bar straight a with rightwards arrow on top cross times space straight b with rightwards arrow on top close vertical bar space equals space square root of left parenthesis negative 17 right parenthesis squared plus left parenthesis 13 right parenthesis squared plus left parenthesis 7 right parenthesis squared end root space equals space 289 plus 169 plus 49 space equals space square root of 507
                     

    Question 485
    CBSEENMA12034167

    Find open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar  if  straight a with rightwards arrow on top space equals straight i with hat on top space minus space 7 space straight j with hat on top space plus space 7 space straight k with hat on top and straight b with rightwards arrow on top space equals space 3 straight i with hat on top space minus space 2 straight j with hat on top space plus space 2 straight k with hat on top

    Solution

    Here,   straight a with rightwards arrow on top space equals straight i with hat on top space minus space 7 space straight j with hat on top space plus space 7 space straight k with hat on top comma space space straight b with rightwards arrow on top space equals 3 space straight i with hat on top space minus space 2 space straight j with hat on top space plus space 2 space straight k with hat on top
    therefore space space space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 1 cell negative 7 end cell 7 row 3 cell negative 2 end cell 2 end table close vertical bar space equals space straight i with hat on top space open vertical bar table row cell negative 7 end cell 7 row cell negative 2 end cell 2 end table close vertical bar space minus space straight j with hat on top space open vertical bar table row 1 7 row 3 2 end table close vertical bar space plus space straight k with hat on top space open vertical bar table row 1 cell negative 7 end cell row 3 cell negative 2 end cell end table close vertical bar
                          equals space left parenthesis negative 14 plus 14 right parenthesis space straight i with hat on top space minus space left parenthesis 2 minus 21 right parenthesis space straight j with hat on top space plus space left parenthesis negative 2 plus 21 right parenthesis space straight k with hat on top space equals space 19 space straight j with hat on top space plus space 19 space straight k with hat on top
    therefore space space space open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar space equals space square root of left parenthesis 0 right parenthesis squared plus left parenthesis 19 right parenthesis squared plus left parenthesis 19 right parenthesis squared end root space equals square root of 0 plus 381 plus 381 end root space equals space square root of 2 space cross times 381 end root space equals space 19 square root of 2

    Question 486
    CBSEENMA12034169

    If straight a with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space minus space 3 space straight k with hat on top space and space straight b with rightwards arrow on top space equals 3 space straight i with hat on top space minus space 2 space straight j with hat on top space plus space 2 space straight k with hat on top comma space space find space open vertical bar 2 straight b with rightwards arrow on top cross times space straight a with rightwards arrow on top close vertical bar.

    Solution
    space straight a with rightwards arrow on top space equals straight i with hat on top space plus space straight j with hat on top space minus space 3 space straight k with hat on top
space straight b with rightwards arrow on top space equals space straight j with hat on top space plus space 2 space straight k with hat on top space space space space space space space space space space space rightwards double arrow space space space space 2 space straight b with rightwards arrow on top space equals space 2 space straight j with hat on top space plus space 4 space straight k with hat on top
    therefore space space 2 space straight b with rightwards arrow on top space cross times space straight a with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 0 2 4 row 1 1 cell negative 3 end cell end table close vertical bar space equals space straight i with hat on top space open vertical bar table row 2 4 row 1 cell negative 3 end cell end table close vertical bar space minus space stack straight j space with hat on top open vertical bar table row 0 4 row 1 cell negative 3 end cell end table close vertical bar space plus straight k with hat on top space open vertical bar table row 0 2 row 1 1 end table close vertical bar
space space space space space space space space space space space space space space space space space space space space space equals space left parenthesis negative 6 minus 4 right parenthesis space straight i with hat on top space minus space left parenthesis 0 minus 4 right parenthesis space straight j with hat on top space plus space left parenthesis 0 minus 2 right parenthesis space straight k with hat on top space equals space minus 10 space straight i with hat on top plus 4 space straight j with hat on top space minus space 2 space straight k with hat on top
                     equals space 2 left parenthesis negative 5 space straight i with hat on top space plus space 2 space straight j with hat on top space minus space straight k with hat on top right parenthesis

    therefore space space space open vertical bar 2 straight b with rightwards arrow on top space cross times space straight a with rightwards arrow on top close vertical bar space equals 2 space square root of left parenthesis negative 5 right parenthesis squared plus left parenthesis 2 right parenthesis squared plus left parenthesis negative 1 right parenthesis squared end root space equals space 2 square root of 25 plus 4 plus 1 end root space equals space 2 square root of 30
    Question 487
    CBSEENMA12034170

    If straight a with rightwards arrow on top space equals straight i with hat on top space minus straight j with hat on top space plus space 2 space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space 3 space straight j with hat on top space minus space 4 space straight k with hat on top comma then show that straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space minus straight b with rightwards arrow on top space cross times space straight a with rightwards arrow on top

    Solution

    Here,    straight a with rightwards arrow on top space equals space straight i with hat on top space minus space straight j with hat on top space plus space 2 space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space 3 space straight j with hat on top space minus space 4 space straight k with hat on top
                          straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 1 cell negative 1 end cell 2 row 2 cell negative 3 end cell cell negative 4 end cell end table close vertical bar space equals space straight i with hat on top space open vertical bar table row cell negative 1 end cell 2 row cell negative 3 end cell cell negative 4 end cell end table close vertical bar space minus space straight j with hat on top space open vertical bar table row 1 2 row 2 cell negative 4 end cell end table close vertical bar space plus straight k with hat on top space open vertical bar table row 1 cell negative 1 end cell row 2 3 end table close vertical bar
space space space space space equals left parenthesis 4 plus 6 right parenthesis space straight i with hat on top space minus space left parenthesis negative 4 minus 4 right parenthesis space straight j with hat on top space plus space left parenthesis negative 3 plus 2 right parenthesis straight j with hat on top
therefore space space space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space 10 space straight i with hat on top space plus space 8 space straight j with hat on top space minus space straight k with hat on top space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis space space space
    Again,   straight b with rightwards arrow on top space cross times space straight a with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 2 cell negative 3 end cell cell negative 4 end cell row 1 cell negative 1 end cell 2 end table close vertical bar space equals space straight i with hat on top space open vertical bar table row cell negative 3 end cell cell negative 4 end cell row cell negative 1 end cell 2 end table close vertical bar space minus space straight j with hat on top space open vertical bar table row 2 cell negative 4 end cell row 1 2 end table close vertical bar space plus space straight k with hat on top space open vertical bar table row 2 cell negative 3 end cell row 1 1 end table close vertical bar
                          equals left parenthesis negative 6 minus 4 right parenthesis space straight i with hat on top space minus space left parenthesis 4 plus 4 right parenthesis space straight j with hat on top space plus space left parenthesis negative 2 plus 3 right parenthesis space straight k with hat on top
equals space minus 10 space straight i with hat on top space minus space 8 space straight j with hat on top space plus space straight k with hat on top space equals space minus left parenthesis 10 straight i with hat on top plus space 8 straight j with hat on top space minus space straight k with hat on top right parenthesis space equals space minus left parenthesis straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top right parenthesis space space space space left square bracket because space of space left parenthesis 1 right parenthesis right square bracket
therefore space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space minus straight b with rightwards arrow on top space cross times space straight a with rightwards arrow on top

    Question 488
    CBSEENMA12034171

    Find a unit vector perpendicular to both straight a with rightwards arrow on top space and space straight b with rightwards arrow on top if  straight a with rightwards arrow on top space equals space 4 space straight i with hat on top space plus space 3 space straight j with hat on top space plus space 2 space straight k with hat on top space space and space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space 5 space straight j with hat on top space minus space 3 space straight k with hat on top

    Solution

    Here,  straight a with rightwards arrow on top space equals 4 space straight i with hat on top space plus space 3 space straight j with hat on top space plus space 2 space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space 5 space straight j with hat on top space minus space 3 space straight k with hat on top
    therefore space space space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 4 3 2 row 2 5 cell negative 3 end cell end table close vertical bar space equals space left parenthesis negative 9 minus 10 right parenthesis space straight i with hat on top space minus space left parenthesis negative 12 minus 4 right parenthesis straight j with hat on top space plus space left parenthesis 20 minus 6 right parenthesis space straight k with hat on top
space space space space equals space minus 19 space straight i with hat on top space plus space 16 space straight j with hat on top space plus 14 space straight k with hat on top
    which is a vector perpendicular to both straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.
    open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar space equals square root of left parenthesis negative 19 right parenthesis squared plus left parenthesis 16 right parenthesis squared plus left parenthesis 14 right parenthesis squared end root space equals square root of 361 plus 256 plus 196 end root space equals square root of 813
    therefore space space space a unit vector perpendicular to straight a with rightwards arrow on top space and space straight b with rightwards arrow on top space equals space fraction numerator straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar end fraction
                                                                    equals space fraction numerator 1 over denominator square root of 813 end fraction left parenthesis negative 19 space straight i with hat on top space plus space 16 space straight j with hat on top space plus space 14 space straight k with hat on top right parenthesis

    Question 489
    CBSEENMA12034172

    Find the unit vector perpendicular to the vectors 
    straight a with rightwards arrow on top space equals space 4 space straight i with hat on top space plus space 3 space straight j with hat on top space minus space straight k with hat on top space and space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space 3 space stack straight j space with hat on top space minus space 3 space straight k with hat on top. 

    Solution
    straight a with rightwards arrow on top space equals space 4 space straight i with hat on top space plus space 3 space straight j with hat on top space minus space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space 3 space straight j with hat on top minus 3 space straight k with hat on top
                  straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 4 3 cell negative 1 end cell row 2 cell negative 3 end cell 3 end table close vertical bar space equals space straight i with hat on top space open vertical bar table row 3 cell negative 1 end cell row cell negative 3 end cell 3 end table close vertical bar space minus space straight j with hat on top space open vertical bar table row 4 cell negative 1 end cell row 2 cell negative 3 end cell end table close vertical bar plus space straight k with hat on top space open vertical bar table row 4 3 row 2 cell negative 3 end cell end table close vertical bar
space space space space space space space space equals space left parenthesis negative 9 minus 3 right parenthesis space straight i with hat on top space minus space left parenthesis negative 12 plus 2 right parenthesis space straight j with hat on top space plus space left parenthesis negative 12 minus 6 right parenthesis space straight k with hat on top
therefore space space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space minus 12 space straight i with hat on top space plus space 10 space straight j with hat on top space minus space 18 space straight k with hat on top
space space space open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar space equals space square root of left parenthesis negative 12 right parenthesis squared plus left parenthesis 10 right parenthesis squared plus left parenthesis negative 18 right parenthesis squared end root space equals space square root of 144 plus 100 plus 324 end root
space space space space space space space space space space space space space space space space space space equals space square root of 568 space equals space square root of 4 space cross times space 142 end root space equals space 2 space square root of 142
    Unit vector perp to vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top space equals space plus-or-minus space fraction numerator straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar end fraction
                                       equals space plus-or-minus space fraction numerator 1 over denominator 2 space square root of 142 end fraction left parenthesis negative 12 space straight i space plus space 10 space straight j with hat on top space minus space 18 space straight k with hat on top right parenthesis space equals space plus-or-minus space fraction numerator 1 over denominator square root of 142 end fraction left parenthesis negative 6 space straight i with hat on top space plus space 5 space straight j with hat on top space minus space 9 space straight k with hat on top right parenthesis
    Question 490
    CBSEENMA12034173

    Find the unit vector perpendicular to vectors 3 straight i with hat on top space plus space straight j with hat on top space minus space 2 space straight k with hat on top comma space space space 2 space straight i with hat on top space plus space straight j with hat on top space minus space straight k with hat on top

    Solution

    Let straight a with rightwards arrow on top space equals space 3 space straight i with hat on top plus straight j with hat on top minus 2 space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals 2 straight i with hat on top space plus space straight j with hat on top space minus space straight k with hat on top
    straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 3 1 cell negative 2 end cell row 2 1 cell negative 2 end cell end table close vertical bar space equals straight i with hat on top space open vertical bar table row 1 cell negative 2 end cell row 1 cell negative 1 end cell end table close vertical bar space minus space straight j with hat on top open vertical bar table row 3 cell negative 2 end cell row 2 cell negative 1 end cell end table close vertical bar space plus space straight k with hat on top space open vertical bar table row 3 1 row 2 1 end table close vertical bar
space space space space space space space space space space space equals left parenthesis negative 1 plus 2 right parenthesis space straight i with hat on top space minus space left parenthesis negative 3 plus 4 right parenthesis space straight j with hat on top space plus space left parenthesis 3 minus 2 right parenthesis space straight k with hat on top equals space straight i with hat on top space minus space straight j with hat on top space plus space straight k with hat on top
therefore space space space open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar space equals square root of 1 plus 1 plus 1 end root space equals square root of 3
    Unit vector perpendicular to straight a with rightwards arrow on top space and space straight b with rightwards arrow on top = plus-or-minus space fraction numerator straight a with rightwards arrow on top cross times space straight b with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar end fraction space equals space plus-or-minus fraction numerator 1 over denominator square root of 3 end fraction left parenthesis straight i with hat on top space minus space straight j with hat on top space plus space straight k with hat on top right parenthesis
                  

    Question 491
    CBSEENMA12034174
    Question 492
    CBSEENMA12034179
    Question 494
    CBSEENMA12034183

    Find a unit vector perpendicular to each of the vector open parentheses straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close parentheses and left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis, where straight a with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top comma space space space space space straight b with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top space plus space space 3 space straight k with hat on top.

    Solution
    straight a with rightwards arrow on top space equals straight i with hat on top plus straight j with hat on top plus straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space straight i with hat on top space plus 2 straight j with hat on top space plus space 3 straight k with hat on top
    therefore space space space space space space space space space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space 3 space straight j with hat on top space plus space 4 space straight k with hat on top comma space space space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space equals space minus straight j with hat on top space minus space 2 space straight k with hat on top
therefore space space space space space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space cross times space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space equals space straight i with hat on top open vertical bar table row 3 4 row cell negative 1 end cell cell negative 2 end cell end table close vertical bar minus space straight j with hat on top space open vertical bar table row 2 4 row 0 cell negative 2 end cell end table close vertical bar space plus space straight k with hat on top space open vertical bar table row 2 3 row 0 cell negative 1 end cell end table close vertical bar
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space left parenthesis negative 6 plus 4 right parenthesis space straight i with hat on top space minus space left parenthesis negative 4 minus 0 right parenthesis space straight j with hat on top space plus space left parenthesis negative 2 minus 0 right parenthesis space straight k with hat on top space equals space minus 2 space straight i with hat on top space plus space 4 space straight j with hat on top space minus space 2 space straight k with hat on top
    which is a vector perpendicular to both open vertical bar left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis space cross times space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis close vertical bar space equals space square root of 4 plus 16 plus 4 end root space equals space square root of 24 space equals space square root of 4 space cross times 6 end root space equals space 2 square root of 6
    therefore space space space required space unit space vector space space equals space fraction numerator left parenthesis straight a with rightwards arrow on top plus space straight b with rightwards arrow on top right parenthesis thin space cross times space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis over denominator open vertical bar left parenthesis straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top right parenthesis space cross times space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis close vertical bar end fraction
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space fraction numerator 1 over denominator 2 square root of 6 end fraction left parenthesis negative 2 space straight i with hat on top space plus space 4 space straight j with hat on top space minus space 2 straight k with hat on top right parenthesis space equals space fraction numerator 1 over denominator square root of 6 end fraction left parenthesis negative straight i with hat on top space plus space 2 space straight j with hat on top space minus space straight k with hat on top right parenthesis
    Question 495
    CBSEENMA12034185

    Find a unit vector perpendicular to each of the vector straight a with rightwards arrow on top plus straight b with rightwards arrow on top space and space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top comma where straight a with rightwards arrow on top space equals space 3 straight i with hat on top space plus space 2 straight j with hat on top space plus space 2 straight k with hat on top and straight b with rightwards arrow on top space equals space straight i with hat on top space plus space 2 straight j with hat on top space minus space 2 space straight k with hat on top.

    Solution

    Here straight a with rightwards arrow on top space equals space 3 straight i with hat on top plus 2 straight j with hat on top plus 2 straight k with hat on top comma space space space space space space straight b with rightwards arrow on top space equals space straight i with hat on top space plus space 2 straight j with hat on top space minus space 2 straight k with hat on top
    therefore space space space space space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space 4 straight i with hat on top space plus space 4 straight j with hat on top comma space space space space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space equals 2 space straight i with hat on top space plus space 4 space straight k with hat on top
    left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis space cross times space space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 4 4 0 row 2 0 4 end table close vertical bar space space equals space straight i with hat on top space open vertical bar table row 4 0 row 0 4 end table close vertical bar space minus space straight j with hat on top space open vertical bar table row 4 0 row 2 4 end table close vertical bar space plus space straight k with hat on top space open vertical bar table row 4 4 row 2 0 end table close vertical bar
space space space space space space space space space space space equals space left parenthesis 16 space minus space 0 right parenthesis space straight i with hat on top space minus space left parenthesis 16 minus 0 right parenthesis space straight j with hat on top space plus space left parenthesis 0 minus 8 right parenthesis space straight k with hat on top space equals space 16 space straight i with hat on top space minus space 16 space straight j with hat on top space minus space 8 space straight k with hat on top
    which is a vector perpendicular to straight a with rightwards arrow on top as well as straight b with rightwards arrow on top.
    left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space cross times space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 4 4 0 row 2 0 4 end table close vertical bar space equals space straight i with hat on top space open vertical bar table row 4 0 row 0 4 end table close vertical bar space minus space straight j with hat on top space open vertical bar table row 4 0 row 2 4 end table close vertical bar space plus space straight k with hat on top space open vertical bar table row 4 4 row 2 0 end table close vertical bar
space space space space space space equals space left parenthesis 16 minus 0 right parenthesis space straight i with hat on top space minus space left parenthesis 16 minus 0 right parenthesis space straight j with hat on top space plus space left parenthesis 0 minus 8 right parenthesis space straight k with hat on top space equals space 16 space straight i with hat on top space minus space 16 space straight j with hat on top space minus 8 space straight k with hat on top
    which is a vector perpendicular to straight a with rightwards arrow on top space as space well space as space straight b with rightwards arrow on top.
    open vertical bar left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis space cross times space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis close vertical bar space equals space square root of left parenthesis 16 right parenthesis squared plus left parenthesis negative 16 right parenthesis squared plus left parenthesis negative 8 right parenthesis squared end root space equals square root of 256 plus 256 plus 64 end root
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space square root of 576 space equals space 24
    therefore a unit vector perpendicular to left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space and space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis is 
                      equals space fraction numerator left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space cross times space left parenthesis straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis over denominator open vertical bar left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space cross times space space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis close vertical bar end fraction space equals space 1 over 24 left parenthesis 16 space straight i with hat on top space minus space 16 space straight j with hat on top space minus space 8 space straight k with hat on top right parenthesis space equals space 1 third left parenthesis 2 straight i with hat on top minus 2 straight j with hat on top minus straight k with hat on top right parenthesis

    Question 496
    CBSEENMA12034186

    Find the value of λ so that the two vectors 2 straight i with hat on top space plus space 3 straight j with hat on top space minus straight k with hat on top and 4 straight i with hat on top plus 6 straight j with hat on top plus straight lambda straight k with hat on top are (i) parallel (ii) perpendicular to each other. 

    Solution

    Let straight a with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space 3 space straight j with hat on top space minus space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space 4 space straight i with hat on top space plus space 6 space straight j with hat on top space plus space straight lambda space straight k with hat on top
       (i)       straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 2 3 cell negative 1 end cell row 4 6 straight lambda end table close vertical bar space equals space straight i with hat on top space open vertical bar table row 3 cell negative 1 end cell row 6 straight lambda end table close vertical bar space minus space straight j with hat on top open vertical bar table row 2 cell negative 1 end cell row 4 straight lambda end table close vertical bar space plus space straight k with hat on top space open vertical bar table row 2 3 row 4 6 end table close vertical bar
                          equals left parenthesis 3 straight lambda plus 6 right parenthesis space straight i with hat on top space minus space left parenthesis 2 straight lambda plus 4 right parenthesis straight j with hat on top plus left parenthesis 12 minus 12 right parenthesis straight k with hat on top space equals space left parenthesis 3 straight lambda plus 6 right parenthesis straight i with hat on top space minus space left parenthesis 2 space straight lambda space plus space 4 right parenthesis straight j with hat on top
    Since straight a with rightwards arrow on top cross times straight b with rightwards arrow on top space equals space 0 with rightwards arrow on top
    therefore space space space left parenthesis 3 straight lambda plus 6 right parenthesis straight i with hat on top space minus space left parenthesis 2 straight lambda plus 4 right parenthesis straight j with hat on top space equals space 0 with rightwards arrow on top
therefore space space space 3 space straight lambda space plus space 6 space equals space 0 comma space space space 2 space straight lambda space plus space 4 space equals space 0 space space space rightwards double arrow space space space straight lambda space equals space minus 2
    (ii) Since straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are perpendiuclar
    therefore space space space straight a with rightwards arrow on top space straight b with rightwards arrow on top space equals space 0
therefore space space space space left parenthesis 2 right parenthesis thin space left parenthesis 4 right parenthesis plus left parenthesis 3 right parenthesis thin space left parenthesis 6 right parenthesis space plus space left parenthesis negative 1 right parenthesis space straight lambda space equals space 8
therefore space space space space 8 plus 18 minus straight lambda space equals space 0 space space space space space space space space space rightwards double arrow space space space space straight lambda space equals space 26
                      
                      

    Question 497
    CBSEENMA12034188

    Find the value of straight lambda so that the two vectors 2 space straight i with hat on top space minus space 4 space straight j with hat on top space plus space straight k with hat on top space space and space 4 space straight i with hat on top space minus space 8 space straight j with hat on top space plus space straight lambda space straight k with hat on top are (i) parallel (ii) perpendicular to each other.

    Solution

    Let straight a with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space 4 space straight j with hat on top space plus space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space 4 space straight i with hat on top space minus space 8 space straight j with hat on top space plus space straight lambda space straight k with hat on top
    (i)  straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 2 cell negative 4 end cell 1 row 4 cell negative 8 end cell straight lambda end table close vertical bar space equals space straight i with hat on top space open vertical bar table row cell negative 4 end cell 1 row cell negative 8 end cell straight lambda end table close vertical bar space minus straight j with hat on top space open vertical bar table row 2 cell negative 1 end cell row 4 cell space space space straight lambda end cell end table close vertical bar space plus space straight k with hat on top space open vertical bar table row 2 cell negative 4 end cell row 4 cell negative 8 end cell end table close vertical bar
                      equals space left parenthesis negative 4 straight lambda plus 8 right parenthesis space straight i with hat on top space minus space left parenthesis 2 straight lambda minus 4 right parenthesis space straight j with hat on top space plus space straight k with hat on top space left parenthesis negative 16 plus 16 right parenthesis space equals space left parenthesis negative 4 space straight lambda space plus 8 right parenthesis straight i with hat on top minus left parenthesis 2 straight lambda minus 4 right parenthesis straight j with hat on top
    Since straight a with rightwards arrow on top space and space straight b with rightwards arrow on top space are space parallel
     therefore space space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space 0 with rightwards arrow on top
    therefore space space left parenthesis negative 4 space straight lambda space plus space 8 right parenthesis space straight i with hat on top space minus space left parenthesis 2 space straight lambda space minus space 4 right parenthesis space straight j with hat on top space equals space 0 with rightwards arrow on top
rightwards double arrow space space space minus 4 straight lambda plus 8 space equals space 0 comma space space space 2 straight lambda minus 4 space equals space 0 space space space space space space rightwards double arrow space space space straight lambda space equals space 2
    (ii) Since straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are perpendicular   
    therefore space space space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0
therefore space space left parenthesis 2 right parenthesis thin space left parenthesis 4 right parenthesis space plus space left parenthesis negative 4 right parenthesis thin space left parenthesis negative 8 right parenthesis space plus space left parenthesis 1 right parenthesis space straight lambda space equals space 0
therefore space space 8 plus 32 plus straight lambda space equals space 0 space space space space space space space space space space space space space space space space space space rightwards double arrow space space space straight lambda space equals space minus 40

    Question 498
    CBSEENMA12034191

    Find the value of straight lambda so that the vectors 2 space straight i with hat on top space plus 4 space straight j with hat on top space minus space 2 space straight k with hat on top and 3 straight i with hat on top space plus space 6 straight j with hat on top space plus space straight lambda straight k with hat on top space are (i) parallel (ii) perpendicular to each other.

    Solution

    Let straight a with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space 4 space straight j with hat on top minus space 2 space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space 3 space straight i with hat on top plus 6 space straight j with hat on top space plus space straight lambda space straight k with hat on top
         straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 2 4 cell negative 2 end cell row 3 6 cell space space straight lambda end cell end table close vertical bar space equals space straight i with hat on top space open vertical bar table row 4 cell negative 2 end cell row 6 cell space space straight lambda end cell end table close vertical bar space minus space straight j with hat on top space open vertical bar table row 2 cell negative 2 end cell row 3 cell space space space straight lambda end cell end table close vertical bar space plus space straight k with hat on top space open vertical bar table row 2 4 row 3 6 end table close vertical bar
space space space space space space space space space space space space equals space left parenthesis 4 straight lambda plus 12 right parenthesis space straight i with hat on top space minus space left parenthesis 2 straight lambda plus 6 right parenthesis straight j with hat on top space plus space left parenthesis 12 minus 12 right parenthesis straight k with hat on top space equals space left parenthesis 4 straight lambda plus 12 right parenthesis straight i with hat on top space minus space left parenthesis 2 straight lambda plus 6 right parenthesis straight j with hat on top
Since space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space are space parallel
therefore space space space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space 0 with rightwards arrow on top
therefore space space space space left parenthesis 4 space straight lambda space plus 12 right parenthesis space straight i with hat on top space minus space left parenthesis 2 straight lambda plus 6 right parenthesis straight j with hat on top space equals 0 with rightwards arrow on top
rightwards double arrow space space 4 straight lambda plus 12 space equals space 0 comma space space 2 straight lambda plus 6 space equals space 0 space space space rightwards double arrow space space space space straight lambda space equals space minus 3
    (ii) Since straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are perpendicular
       therefore space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0
therefore space space space left parenthesis 2 right parenthesis thin space left parenthesis 3 right parenthesis space plus space left parenthesis 4 right parenthesis thin space left parenthesis 6 right parenthesis space plus space left parenthesis negative 2 right parenthesis space straight lambda space equals space 0
therefore space space space 6 plus 24 minus 2 straight lambda space equals space 0 space space space space space space space space space space space space space space space space space space space rightwards double arrow space 2 space straight lambda space equals 30 space space space space space space space space space space space space space space space space rightwards double arrow space space space space straight lambda space equals space 15

    Question 499
    CBSEENMA12034193

    Find a vector of magnitude 9 and which is perpendicular to both the vectors
    straight a with rightwards arrow on top space equals space 4 straight i with hat on top space minus space straight j with hat on top space plus space 3 space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space minus 2 space straight i with hat on top space space plus space straight j with hat on top space minus space 2 space straight k with hat on top
     

    Solution

    Here straight a with rightwards arrow on top space equals space 4 space straight i with hat on top space minus space straight j with hat on top space plus space 3 space straight k with hat on top comma space space space space straight b with rightwards arrow on top space equals space minus 2 space straight i with hat on top space plus space straight j with hat on top space minus space 2 space straight k with hat on top
    therefore space straight a with rightwards arrow on top cross times straight b with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 4 cell negative 1 end cell 3 row cell negative 2 end cell cell negative 1 end cell cell negative 2 end cell end table close vertical bar space equals space straight i with hat on top space open vertical bar table row cell negative 1 end cell 3 row 1 cell negative 2 end cell end table close vertical bar space minus straight j with hat on top space open vertical bar table row 4 3 row cell negative 2 end cell cell negative 2 end cell end table close vertical bar plus space straight k with hat on top space open vertical bar table row 4 cell negative 1 end cell row 2 cell negative 1 end cell end table close vertical bar
space space space space space space space space space space space space space space space space equals space left parenthesis 2 minus 3 right parenthesis space straight i with hat on top space minus space left parenthesis negative 8 plus 6 right parenthesis space straight j with hat on top space plus space left parenthesis 4 minus 2 right parenthesis space straight k with hat on top space equals space minus straight i with hat on top space plus space 2 space straight j with hat on top space plus space 2 space straight k with hat on top
    which is vector perpendicular to straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.
    open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar space equals space square root of 1 plus 4 plus 4 end root space equals space square root of 9 space equals space 3
    therefore space space space a unit vector perpendicular to straight a with rightwards arrow on top space and space straight b with rightwards arrow on top is equals space fraction numerator straight a with rightwards arrow on top cross times straight b with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top cross times space straight b with rightwards arrow on top close vertical bar end fraction space equals 1 third left parenthesis negative straight i with hat on top plus 2 space straight j with hat on top space plus space space 2 space straight k with hat on top right parenthesis
               therefore   a vector of magnitude 9 and perp. to straight a with rightwards arrow on top space and space straight b with rightwards arrow on top  is
                                          equals space 9 space open parentheses fraction numerator straight a with rightwards arrow on top cross times straight b with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar end fraction close parentheses space equals 9 over 3 left parenthesis negative straight i with hat on top space plus space 2 space straight j with hat on top space plus space 2 space straight k with hat on top right parenthesis space equals space 3 space left parenthesis negative straight i with hat on top space plus space 2 straight j with hat on top space plus 2 straight k with hat on top right parenthesis
    Required vector can be  = negative 3 left parenthesis negative straight i with hat on top space plus 2 space straight j with hat on top space plus space 2 space straight k with hat on top right parenthesis.

    Question 500
    CBSEENMA12034195

    Find a vector of magnitude 19 and which is perpendicular to both the vectors 4 space straight i with hat on top space minus space straight j with hat on top space plus space 8 space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space minus straight j with hat on top space plus space straight k with hat on top

    Solution

    Let straight a with rightwards arrow on top space equals space 4 space straight i with hat on top space minus space straight j with hat on top space plus space 8 space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space minus straight j with hat on top space plus space straight k with hat on top
    straight a with rightwards arrow on top cross times straight b with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 4 cell negative 1 end cell 8 row 0 cell negative 1 end cell 1 end table close vertical bar space equals straight i with hat on top space open vertical bar table row cell negative 1 end cell 8 row cell negative 1 end cell 1 end table close vertical bar space minus straight j with hat on top space open vertical bar table row 4 8 row 0 1 end table close vertical bar plus space straight k with hat on top open vertical bar table row 4 cell negative 1 end cell row 0 cell negative 1 end cell end table close vertical bar
                equals left parenthesis negative 1 plus 8 right parenthesis space straight i with hat on top space minus left parenthesis 4 minus 0 right parenthesis space straight j with hat on top plus left parenthesis negative 4 plus 0 right parenthesis space straight k with hat on top space equals space 7 space straight i with hat on top space minus space 4 space straight j with hat on top space minus space 4 space straight k with hat on top
    which is vector perpendicular to straight a with rightwards arrow on top space and space straight b with rightwards arrow on top .
                  open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar space equals space square root of left parenthesis 7 right parenthesis squared plus left parenthesis negative 4 right parenthesis squared plus left parenthesis negative 4 right parenthesis squared end root space equals space square root of 49 plus 16 plus 16 end root space equals square root of 81 space equals space 9
    therefore a unit vector perpendicular to straight a with rightwards arrow on top space and space straight b with rightwards arrow on top is
                         equals space fraction numerator straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top cross times space straight b with rightwards arrow on top close vertical bar end fraction space equals space 1 over 9 left parenthesis 7 straight i with hat on top space minus 4 space straight j with hat on top space minus space 4 straight k with hat on top right parenthesis
    therefore a vector of magnitude of 19 and perpendicular to straight a with rightwards arrow on top space and space straight b with rightwards arrow on top is 
                                 equals 19 space open parentheses fraction numerator straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar end fraction close parentheses space equals 19 over 9 left parenthesis 7 space straight i with hat on top space minus space 4 space straight j with hat on top space minus space 4 space straight k with hat on top right parenthesis

    Question 501
    CBSEENMA12034197

    Find a vector of magnitude 5 units, perpendicular to each of the vectors
    left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space and space left parenthesis straight a with rightwards arrow on top space minus straight b with rightwards arrow on top right parenthesis where straight a with rightwards arrow on top space equals space straight i with hat on top plus straight j with hat on top plus straight k with hat on top and straight b with rightwards arrow on top space equals space straight i with hat on top space plus space 2 straight j with hat on top space plus 3 straight k with hat on top.

    Solution

    Here,   straight a with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space straight i with hat on top space plus 2 space straight j with hat on top space plus space 3 space straight k with hat on top.
    therefore space space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space equals space straight i with hat on top space plus straight j with hat on top space plus straight k with hat on top space space plus straight i with hat on top space plus space 2 space straight j with hat on top plus 3 space straight k with hat on top space equals space 2 space straight i with hat on top plus 3 space straight j with hat on top plus 4 space straight k with hat on top
    and  straight a with rightwards arrow on top minus straight b with rightwards arrow on top space equals space straight i with hat on top plus straight j with hat on top plus straight k with hat on top minus straight i with hat on top minus 2 straight j with hat on top minus 3 straight k with hat on top space equals space minus straight j with hat on top minus 2 straight k with hat on top
    therefore space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis thin space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 2 3 4 row 0 cell negative 1 end cell cell negative 2 end cell end table close vertical bar
                           equals space straight i with hat on top space open vertical bar table row cell space space space 3 end cell cell space space space 4 end cell row cell negative 1 end cell cell negative 2 end cell end table close vertical bar space minus space straight j with hat on top space open vertical bar table row 2 4 row 0 cell negative 2 end cell end table close vertical bar space plus straight k with hat on top space open vertical bar table row 2 3 row 0 cell negative 1 end cell end table close vertical bar
equals space left parenthesis negative 6 plus 4 right parenthesis space straight i with hat on top space minus space left parenthesis negative 4 minus 0 right parenthesis space straight j with hat on top space plus space left parenthesis negative 2 plus 0 right parenthesis space straight k with hat on top space equals space minus 2 space straight i with hat on top space plus space 4 space straight j with hat on top space minus space 2 space straight k with hat on top
    which is a vector perpendicular to straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.
    therefore space space space space open vertical bar left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space cross times space space left parenthesis straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis close vertical bar space equals space square root of left parenthesis negative 2 right parenthesis squared plus left parenthesis 4 right parenthesis squared plus left parenthesis negative 2 right parenthesis squared end root space equals space square root of 4 plus 16 plus 4 end root space equals space square root of 24
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space square root of 4 space cross times 6 end root space equals 2 square root of 6
    therefore space space space a unit vector perpendicular to left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space and space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis
                                 equals space fraction numerator left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space cross times space left parenthesis straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis over denominator open vertical bar left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space cross times space left parenthesis straight a with rightwards arrow on top space minus straight b with rightwards arrow on top right parenthesis close vertical bar end fraction space equals space fraction numerator 1 over denominator 2 square root of 6 end fraction left parenthesis negative 2 space straight i with hat on top space plus space 4 space straight j with hat on top space minus space 2 space straight k with hat on top right parenthesis
    therefore vector of magnitude 5 units and perpendicular to left parenthesis straight a with rightwards arrow on top plus space straight b with rightwards arrow on top right parenthesis space and space left parenthesis straight a with rightwards arrow on top space minus stack straight b right parenthesis with rightwards arrow on top is
                                            equals space 5 space open parentheses fraction numerator left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space cross times space left parenthesis straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis over denominator open vertical bar left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space cross times space left parenthesis straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis close vertical bar end fraction close parentheses space equals space fraction numerator 5 over denominator 2 square root of 6 end fraction left parenthesis negative 2 space straight i with hat on top space plus space 4 space straight j with hat on top space minus space 2 space straight k with hat on top right parenthesis
equals space minus fraction numerator 5 over denominator square root of 6 end fraction straight i with hat on top space plus space fraction numerator 10 over denominator square root of 6 end fraction straight j with hat on top space minus space fraction numerator 5 over denominator square root of 6 end fraction straight k with hat on top

    Question 502
    CBSEENMA12034198
    Question 503
    CBSEENMA12034200
    Question 505
    CBSEENMA12034203

    If open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 5 comma space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 4 space and space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 16 comma space find space open vertical bar straight a with rightwards arrow on top cross times space straight b with rightwards arrow on top close vertical bar.

    Solution

    Here open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 5 comma space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals 4
    Also,  straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 16
    therefore space space space open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar space cos space straight theta space equals space 16 space where space straight theta space is space angle space between space straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.
    therefore space space space left parenthesis 5 right parenthesis thin space left parenthesis 4 right parenthesis space cos space straight theta space equals space 16 space space space space space rightwards double arrow space space space space cos space straight theta space equals space 16 over 20 space equals space 4 over 5
rightwards double arrow space space space space space space space space space space space space space space space space space space space space space space space space sin space straight theta space equals space 3 over 5
therefore space space space open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar space sin space straight theta space equals space left parenthesis 5 right parenthesis thin space left parenthesis 4 right parenthesis space open parentheses 3 over 5 close parentheses space equals space 12

    Question 506
    CBSEENMA12034204

    Find open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar if   open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 10 comma space space space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 2 space space and space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 12.

    Solution

    We have open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 10 comma space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 2
    Also,    straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 12
    therefore space space space open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar space cos space straight theta space equals space 12 comma
    where straight theta is an angle between straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.
    therefore space space space left parenthesis 10 right parenthesis thin space left parenthesis 2 right parenthesis space cos space straight theta space equals space 12 space space space space space rightwards double arrow space space space space cos space equals space 12 over 20 space equals 3 over 5
rightwards double arrow space space space sin space straight theta space equals space 4 over 5
Now space space open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight a with rightwards arrow on top close vertical bar space cross times space open vertical bar straight b with rightwards arrow on top close vertical bar space sin space straight theta
space space space space space space space space space space space space space space space space space space space space space space space space space equals space left parenthesis 10 right parenthesis thin space left parenthesis 2 right parenthesis thin space open parentheses 4 over 5 close parentheses space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
space space space space space space space space space space space space space space space space space space space space space space space space space space equals space 16

    Question 507
    CBSEENMA12034206

    Use vector method only to find the values of a and b if points (2, b, 3), (a, – 5, 1) and ( – 1, 11, 9) are collinear.

    Solution
    Let A (2, b, 3), B (a. – 5, 1) and C (– 1, 11, 9) be given points.
    AB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A space equals space open parentheses straight a space straight i with hat on top space minus space 5 space straight j with hat on top space plus space straight k with hat on top close parentheses space minus space left parenthesis 2 space straight i with hat on top space plus space straight b space straight j with hat on top plus space 3 space straight k with hat on top right parenthesis
space space space space space space equals space left parenthesis straight a minus 2 right parenthesis space straight i with hat on top space minus space left parenthesis straight b plus 5 right parenthesis space straight j with hat on top space space minus space 2 space straight k with hat on top
AC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight A space equals space open parentheses negative straight i with hat on top space plus 11 stack straight j space with hat on top plus 9 space straight k with hat on top close parentheses space minus space left parenthesis 2 space straight i with hat on top space plus space straight b space straight j with hat on top space plus space 3 space straight k with hat on top right parenthesis
space space space space space space space equals negative 3 straight i with hat on top space plus space left parenthesis 11 minus straight b right parenthesis space straight j with hat on top space plus space 6 space straight k with hat on top
    Since A, B, C are collinear
    therefore space space space open vertical bar AB with rightwards arrow on top space cross times space AC with rightwards arrow on top space close vertical bar space equals space 0 with rightwards arrow on top
therefore space space space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row cell straight a minus 2 end cell cell negative straight b minus 5 end cell cell negative 2 end cell row cell negative 3 end cell cell 11 minus straight b end cell 6 end table close vertical bar space equals space 0 with rightwards arrow on top
rightwards double arrow space space space space open vertical bar table row cell negative straight b minus 5 end cell cell space minus 2 end cell row cell 11 minus straight b end cell cell space space space 6 end cell end table close vertical bar space straight i with hat on top space minus space open vertical bar table row cell straight a minus 2 end cell cell space minus 2 end cell row cell negative 3 end cell cell space space space 6 end cell end table close vertical bar straight j with hat on top space plus space open vertical bar table row cell straight a minus 2 space space space end cell cell negative straight b minus 5 end cell row cell negative 3 end cell cell space 11 minus straight b end cell end table close vertical bar straight k with hat on top space equals 0 with rightwards arrow on top
therefore space space space space space left parenthesis negative 6 straight b minus 30 space plus 22 space minus 2 straight b right parenthesis straight i with hat on top space minus space left parenthesis 6 straight a minus 12 minus 6 right parenthesis space straight j with hat on top space plus space open square brackets left parenthesis straight a minus 2 right parenthesis thin space left parenthesis 1 minus straight b right parenthesis space plus 3 space left parenthesis straight b minus 5 right parenthesis close square brackets straight k with hat on top space equals space 0
therefore space space space space minus 6 straight b minus 30 plus 22 minus 2 straight b space equals space 0 comma space space space space 6 straight a minus 12 minus 6 space equals space 0
therefore space space space space space minus 8 straight b space equals space 8 comma space space space 6 straight a space equals 18
rightwards double arrow space space space space space space straight b space equals space minus 1 comma space space space straight a space equals space 3 space space space space space rightwards double arrow space space space space straight a space equals space 3 comma space space space straight b space equals space minus 1
    Question 510
    CBSEENMA12034209

    Find the area of the parallelogram determined by the vectors 3 space straight i with hat on top space plus space 4 space straight j with hat on top space and space straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top.

    Solution

    Let straight a with rightwards arrow on top space equals space 3 straight i with hat on top plus 4 straight j with hat on top comma space space space straight b with rightwards arrow on top space equals space straight i with hat on top space plus straight j with hat on top space plus space straight k with hat on top
                 straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 3 4 0 row 1 1 1 end table close vertical bar space equals space straight i with hat on top space open vertical bar table row 4 0 row 1 1 end table close vertical bar space minus space straight j with hat on top space open vertical bar table row 3 0 row 1 1 end table close vertical bar plus straight k with hat on top space open vertical bar table row 3 4 row 1 1 end table close vertical bar
space space space space space space space space space space space space space space equals left parenthesis 4 minus 0 right parenthesis space straight i with hat on top space minus space left parenthesis 3 minus 0 right parenthesis space straight j with hat on top space plus space left parenthesis 3 minus 4 right parenthesis space straight k with hat on top space equals space 4 space straight i with hat on top space minus space 3 space straight j with hat on top space minus space straight k with hat on top
therefore space space space space space space open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar space equals space square root of 16 plus 9 plus 1 end root space equals space square root of 26
therefore space space area space of space parallelogram space equals space square root of 26 space sq. space units. space

    Question 512
    CBSEENMA12034212

    Determine the area of the parallelogram, whose adjacent sides are given by the vectors
    straight i with hat on top minus straight j with hat on top minus straight k with hat on top space and space space 3 space straight i with hat on top space plus space 4 space straight j with hat on top space minus space 5 space straight k with hat on top.

    Solution

    Let     straight a with rightwards arrow on top space equals space straight i with hat on top space minus space straight j with hat on top space minus space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space 3 space straight i with hat on top space plus space 4 space straight j with hat on top space minus space 5 space straight k with hat on top
    straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell space space space straight j with hat on top end cell cell straight k with hat on top end cell row 1 cell negative 1 end cell cell negative 1 end cell row 3 cell space space 4 end cell cell negative 5 end cell end table close vertical bar
                             equals straight i with hat on top space open vertical bar table row cell negative 1 end cell cell negative 1 end cell row 4 cell negative 5 end cell end table close vertical bar space minus space straight j with hat on top space open vertical bar table row 1 cell negative 1 end cell row 3 cell negative 5 end cell end table close vertical bar space plus straight k with hat on top space open vertical bar table row 1 cell negative 1 end cell row 3 4 end table close vertical bar
equals space left parenthesis 5 plus 4 right parenthesis space straight i with hat on top space minus space left parenthesis negative 5 plus 3 right parenthesis space straight j with hat on top space plus space left parenthesis 4 plus 3 right parenthesis space straight k with hat on top space equals space 9 space straight i with hat on top space plus space 2 space straight j with hat on top space plus space 7 space straight k with hat on top
    open vertical bar straight a with rightwards arrow on top space cross times straight b with rightwards arrow on top close vertical bar space equals space square root of left parenthesis 9 right parenthesis squared plus left parenthesis 2 right parenthesis squared plus left parenthesis 7 right parenthesis squared end root space equals space square root of 81 plus 4 plus 49 end root space equals space square root of 134
    therefore space space space area space of space parallelogram space equals space open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar space equals space square root of 134 space sq. space units.

    Question 513
    CBSEENMA12034214
    Question 514
    CBSEENMA12034215

    The two adjacent sides of a parallelogram are 2 straight i with hat on top minus 4 straight j with hat on top plus 5 straight k with hat on top and straight i with hat on top space minus space 2 space straight j with hat on top space minus space 3 space straight k with hat on top.
    Find the unit vector parallel to its diagonal. Also find its area.

    Solution
    Let ABCD be the parallelogram with
                     AB with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space 4 space straight j with hat on top space plus space 5 space straight k with hat on top space and space AD with rightwards arrow on top space equals straight i with hat on top minus 2 space straight j with hat on top minus 3 space straight k with hat on top
    Now   AC with rightwards arrow on top space equals space AB with rightwards arrow on top space plus space BC with rightwards arrow on top space equals space AB with rightwards arrow on top space plus space AD with rightwards arrow on top
                          equals left parenthesis 2 space straight i with hat on top space minus space 4 space straight j with hat on top space plus space 5 space straight k with hat on top right parenthesis plus left parenthesis straight i with hat on top minus 2 space straight j with hat on top space minus space 3 space straight k with hat on top right parenthesis space equals space 3 space straight i with hat on top space minus space 6 space straight j with hat on top space plus space 2 space straight k with hat on top
    Here a unit vector parallel to 
    AC with rightwards arrow on top space equals space fraction numerator 1 over denominator open vertical bar AC with rightwards arrow on top close vertical bar end fraction left parenthesis stack AC right parenthesis with rightwards arrow on top
space space space space equals space fraction numerator 1 over denominator square root of 3 squared plus left parenthesis negative 6 right parenthesis squared plus 2 squared end root end fraction left parenthesis 3 straight i with hat on top minus 6 straight j with hat on top space plus space 2 straight k with hat on top right parenthesis
space space equals space fraction numerator 1 over denominator square root of 9 plus 36 plus 4 end root end fraction left parenthesis 3 space straight i with hat on top space minus space 6 space straight j with hat on top space space plus space 2 space straight k with hat on top right parenthesis space equals space fraction numerator 1 over denominator square root of 49 end fraction left parenthesis 3 straight i with hat on top space minus space 6 straight j with hat on top space plus space 2 straight k with hat on top right parenthesis
space equals space 1 over 7 left parenthesis 3 straight i with hat on top space minus space 6 straight j with hat on top space plus space 2 straight k with hat on top right parenthesis space equals space 3 over 7 straight i with hat on top space minus space 6 over 7 straight j with hat on top space plus space 2 over 7 straight k with hat on top
    Vector area of parallelogram ABCD = AB with rightwards arrow on top space cross times space AD with rightwards arrow on top
                         equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell space space straight k with hat on top end cell row 2 cell negative 4 end cell cell space space 5 end cell row 1 cell negative 2 end cell cell negative 3 end cell end table close vertical bar space equals space straight i with hat on top space open vertical bar table row cell negative 4 end cell cell space space space space 5 end cell row cell negative 2 end cell cell space minus 3 end cell end table close vertical bar space minus space straight j with hat on top space open vertical bar table row 2 5 row 1 cell negative 3 end cell end table close vertical bar space plus space straight k with hat on top space open vertical bar table row 2 cell negative 4 end cell row 1 cell negative 2 end cell end table close vertical bar
equals space straight i with hat on top left parenthesis 12 plus 10 right parenthesis space minus space straight j with hat on top left parenthesis 6 minus 5 right parenthesis space plus space straight k with hat on top left parenthesis negative 4 plus 4 right parenthesis
equals space 22 straight i with hat on top space plus 11 space straight j with hat on top space plus space 0 space straight k with hat on top
therefore space area space of space parallelogram space equals space open vertical bar AB with rightwards arrow on top space cross times AD with rightwards arrow on top close vertical bar space equals space open vertical bar 22 space straight i with hat on top space plus space 11 space straight j with hat on top space plus space 0 space straight k with hat on top close vertical bar
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals square root of left parenthesis 22 right parenthesis squared plus left parenthesis 11 right parenthesis squared plus 0 squared end root space equals space square root of 484 plus 121 plus 0 end root
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space square root of 605 space equals space square root of 21 space cross times 5 end root space space equals space 11 square root of 5 space space sq. space units.

    Question 515
    CBSEENMA12034216

    Find the area of the parallelogram whose diagonals are
    straight a with rightwards arrow on top space equals space 3 space straight i with hat on top space plus space straight j with hat on top space minus space 2 space straight k with hat on top space space space and space straight b with rightwards arrow on top space equals space straight i with hat on top space minus space 3 space straight j with hat on top space plus space 4 space straight k with hat on top.

    Solution
    Let ABCD be the parallelogram such that
    straight a with rightwards arrow on top space equals space AC with rightwards arrow on top space equals space 3 straight i with hat on top space plus space straight j with hat on top space minus space 2 space straight k with hat on top comma space space space space straight b with rightwards arrow on top space equals space BD with rightwards arrow on top space equals space straight i with hat on top space minus space 3 space straight j with hat on top space plus space 4 space straight k with hat on top
                Vectors of || gm ABCD = Vector area of ∆ ABC + Vector area of ∆ ACD

                    equals space 1 half AB with rightwards arrow on top space cross times space AC with rightwards arrow on top space plus space 1 half AC with rightwards arrow on top space cross times space AD with rightwards arrow on top
equals space 1 half left parenthesis negative AC with rightwards arrow on top space cross times space AB with rightwards arrow on top space plus space AC with rightwards arrow on top space cross times space AD with rightwards arrow on top right parenthesis
equals space 1 half AC with rightwards arrow on top space cross times space left parenthesis negative AB with rightwards arrow on top space plus space AD with rightwards arrow on top right parenthesis
equals space 1 half AC with rightwards arrow on top space cross times space left parenthesis BA with rightwards arrow on top space plus space AD with rightwards arrow on top right parenthesis space equals space 1 half AC with rightwards arrow on top space cross times space BD with rightwards arrow on top space equals space 1 half straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top
equals space 1 half left parenthesis 3 straight i with hat on top space plus space space straight j with hat on top minus space 2 space straight k with hat on top right parenthesis space cross times left parenthesis straight i with hat on top space minus space 3 space straight j with hat on top space plus space 4 space straight k with hat on top right parenthesis
space equals space 1 half open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 3 1 cell negative 2 end cell row 1 cell negative 3 end cell cell space 4 end cell end table close vertical bar space equals space 1 half left square bracket left parenthesis 4 minus 6 right parenthesis space straight i with hat on top space minus space left parenthesis 12 plus 2 right parenthesis space straight j with hat on top plus space left parenthesis negative 5 minus 1 right parenthesis straight k with hat on top
equals space 1 half left parenthesis negative 2 space straight i with hat on top space plus space 14 space straight j with hat on top space minus space 10 space straight k with hat on top right parenthesis space equals space minus straight i with hat on top space minus space 7 space straight j with hat on top space minus space 5 space straight k with hat on top
therefore space space space area space of space vertical line vertical line space gm thin space ABCD space equals space open vertical bar negative straight i with hat on top minus 7 space straight j with hat on top space minus space 5 space straight k with hat on top close vertical bar space equals square root of 1 plus 49 plus 25 end root space equals square root of 75 space equals space 5 space square root of 3 space sq. space units. space
    Question 516
    CBSEENMA12034218

    Find the area of the triangle whose adjacent sides are made by the vectors 

    Solution
    straight a with rightwards arrow on top space equals space 3 space straight i with hat on top space plus space straight j with hat on top space plus space 4 space straight k with hat on top comma space space space space straight b with rightwards arrow on top space equals space straight i with hat on top space minus space straight j with hat on top space plus space straight k with hat on top
                    straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 3 1 4 row 1 cell negative 1 end cell 1 end table close vertical bar space equals space straight i with hat on top space open vertical bar table row 1 4 row cell negative 1 end cell 1 end table close vertical bar space minus straight j with hat on top space open vertical bar table row 3 4 row 1 1 end table close vertical bar space plus space straight k with hat on top space open vertical bar table row 3 1 row 1 cell negative 1 end cell end table close vertical bar
space space space space space space space space space space space space space equals space left parenthesis 1 plus 4 right parenthesis space straight j with hat on top space minus space left parenthesis 3 minus 4 right parenthesis space straight j with hat on top space plus left parenthesis negative 3 minus 1 right parenthesis space straight k with hat on top space equals space 5 space straight i with hat on top space plus space straight j with hat on top space minus 4 space straight k with hat on top
space therefore space space open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar space equals space square root of 25 plus 1 plus 16 end root space equals space square root of 42
    Required area of triangle  = 1 half open vertical bar straight a with rightwards arrow on top cross times straight b with rightwards arrow on top close vertical bar space equals space 1 half square root of 42 space sq. space units.
    Question 518
    CBSEENMA12034221

    Find the vectors area and also the scalar area of a triangle, the position vectors of whose vertices are negative straight i with hat on top plus straight j with hat on top plus 3 space straight k with hat on top comma space straight i with hat on top plus 2 space straight j with hat on top space plus space 4 space straight k with hat on top space and space 2 space straight i with hat on top space minus space straight j with hat on top space plus space straight k with hat on top.

    Solution

    Let straight a with rightwards arrow on top space equals space minus straight i with hat on top plus straight j with hat on top plus 3 straight k with hat on top comma space space straight b with rightwards arrow on top space equals 3 space straight i with hat on top space plus space 2 space straight j with hat on top space plus space 4 space straight k with hat on top comma space space straight c with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space straight j with hat on top space plus space straight k with hat on top
    be P.Vs. of A, B and C respectively.
    BC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight B space equals space straight c with rightwards arrow on top minus straight b with rightwards arrow on top space equals space minus straight i with hat on top minus 3 space straight j with hat on top space minus space 3 space straight k with hat on top
BA with rightwards arrow on top space equals space straight P. straight V. space of space straight A space minus space straight P. straight V. space of space straight B space equals space straight a with rightwards arrow on top minus straight b with rightwards arrow on top space equals space minus 4 space straight i with hat on top space minus space straight j with hat on top space minus space straight k with hat on top
space space space BC with rightwards arrow on top space cross times BA with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell space space straight j with hat on top end cell cell space space straight k with hat on top end cell row cell negative 1 end cell cell space minus 3 end cell cell space space minus 3 end cell row cell negative 4 space end cell cell negative 1 end cell cell negative 1 end cell end table close vertical bar
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals left parenthesis 3 minus 3 right parenthesis straight i with hat on top minus left parenthesis 1 minus 12 right parenthesis space straight j with hat on top space plus space left parenthesis 1 minus 12 right parenthesis space straight k with hat on top space equals space 11 space straight j with hat on top space minus space space 11 space straight k with hat on top
    therefore space space vector space area space of space increment ABC space equals space 1 half space BC with rightwards arrow on top space cross times BA with rightwards arrow on top space equals space 1 half left parenthesis 11 space straight j with hat on top space minus space 11 space straight k with hat on top right parenthesis space equals space 11 over 2 left parenthesis straight j with hat on top minus straight k with hat on top right parenthesis
           Scalar area of increment ABC = open vertical bar 11 over 2 left parenthesis straight j with hat on top space minus space straight k with hat on top right parenthesis close vertical bar space equals space 11 over 2 square root of left parenthesis 1 right parenthesis squared plus left parenthesis negative 1 right parenthesis squared end root space equals space 11 over 2 square root of 2 space equals fraction numerator 11 over denominator square root of 2 end fraction

    Question 519
    CBSEENMA12034223

    Find the area of the triangle formed by the points A (1, 1, 1), B (1, 2, 3) and C (2, 3, 1) with reference to a rectangular system of axes.

    Solution
    The given vertices are A (1, 1, 1), B (1, 2. 3) and C (2, 3, 1).
      Let straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top be the position vectors of A, B, C respectively.
    therefore space space space straight a with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top comma space space space space straight b with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top space plus space 3 space straight k with hat on top comma space space straight c with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space 3 space straight j with hat on top space plus space straight k with hat on top
    Now,       BC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight B space equals space straight c with rightwards arrow on top space minus space straight b with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space minus 2 space straight k with hat on top
                   BA with rightwards arrow on top space equals space straight P. straight V. space of space straight A space minus space straight P. straight V. space of space straight B space equals space straight a with rightwards arrow on top space space minus straight b with rightwards arrow on top space equals space minus straight j with hat on top space minus space 2 space straight k with hat on top
           BC with rightwards arrow on top space cross times space BA with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell space straight j with hat on top end cell cell space space space straight k with hat on top end cell row 1 cell space 1 end cell cell negative 2 end cell row 0 cell negative 1 end cell cell negative 2 end cell end table close vertical bar space equals space straight i with hat on top space open vertical bar table row cell space space 1 end cell cell space space minus 2 end cell row cell negative 1 end cell cell space space minus 2 end cell end table close vertical bar space minus space straight j with hat on top space open vertical bar table row 1 cell negative 2 end cell row 0 cell negative 2 end cell end table close vertical bar space plus straight k with hat on top space open vertical bar table row 1 cell space space space 1 end cell row 0 cell negative 1 end cell end table close vertical bar
space space space space space space space space space space space space space space space space equals space left parenthesis negative 2 minus 4 right parenthesis space straight i with hat on top space minus space left parenthesis negative 2 minus 0 right parenthesis space straight j with hat on top space plus space left parenthesis negative 1 minus 0 right parenthesis space straight k with hat on top space equals space minus 4 space straight i with hat on top space plus space 2 space straight j with hat on top space minus space straight k with hat on top
therefore space space space space open vertical bar BC with rightwards arrow on top space cross times space BA with rightwards arrow on top close vertical bar space equals space square root of 16 plus 4 plus 1 end root space equals space square root of 21
Area space of space increment ABC space equals space 1 half open vertical bar BC with rightwards arrow on top space cross times space BA with rightwards arrow on top close vertical bar space equals space 1 half square root of 21 space sq. space units.
    Question 520
    CBSEENMA12034225

    Find the area of the triangle with vertices (1, 1, 2), (2, 3, 5) and (1, 5, 5). 

    Solution

    Let straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top be position vectors of A, B, C repsectively.
    therefore space space space space straight a with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space plus space 2 space straight k with hat on top comma space space space space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space 3 space straight j with hat on top space plus space 5 space straight k with hat on top comma space space straight c with rightwards arrow on top space equals straight i with hat on top space plus space 5 space straight j with hat on top space plus space 5 space straight k with hat on top
    Now, BC with rightwards arrow on top space equals straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight B space equals straight c with rightwards arrow on top minus straight b with rightwards arrow on top space equals space minus straight i with hat on top space plus space 2 space straight j with hat on top
              BA with rightwards arrow on top space equals space straight P. straight V. space of space straight A space minus space straight P. straight V. space of thin space straight B space equals space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space equals space minus straight i with hat on top space minus space 2 space straight j with hat on top space minus space 3 space straight k with hat on top
    therefore space space space space BC with rightwards arrow on top space cross times space BA with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell space space straight j with hat on top end cell cell space space straight k with hat on top end cell row cell negative 1 end cell cell space space space space 2 end cell cell space space 0 end cell row cell negative 1 end cell cell space minus 2 end cell cell negative 3 end cell end table close vertical bar space equals space straight i with hat on top space open vertical bar table row cell space space space 2 end cell 0 row cell negative 2 end cell cell negative 3 end cell end table close vertical bar minus space straight j with hat on top space open vertical bar table row cell negative 1 end cell 0 row cell negative 1 end cell cell negative 3 end cell end table close vertical bar plus space straight k with hat on top space open vertical bar table row cell negative 1 end cell 2 row cell negative 1 end cell cell negative 2 end cell end table close vertical bar
space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space left parenthesis negative 6 minus 0 right parenthesis space straight i with hat on top space minus space left parenthesis 3 minus 0 right parenthesis space straight j with hat on top space plus space left parenthesis 2 plus 2 right parenthesis space straight k with hat on top space equals space minus 6 space straight i with hat on top space minus space 3 space straight j with hat on top space plus space 4 space straight k with hat on top
space space space space space space space space space space space space space space open vertical bar BC with rightwards arrow on top space cross times space BA with rightwards arrow on top close vertical bar space equals space square root of 36 plus 9 plus 16 end root space equals space square root of 61
    Area of increment ABC space equals space 1 half open vertical bar BC with rightwards arrow on top space cross times space BA with rightwards arrow on top close vertical bar space equals space 1 half square root of 61 space sq. space units

    Question 521
    CBSEENMA12034228

    Find the area of the triangle (by vectors) with vertices
    A (3, – 1, 2), B (1, – 1, – 3) and C (4, – 3, 1).

    Solution
    Given vertices are A (3, – 1, 2) , B (1, – 1, – 3), C (4, – 3, 1 ).
    Let straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top be position vectors of A, B, C respectively.
    therefore space space space straight a with rightwards arrow on top space equals space 3 space straight i with hat on top space minus space straight j with hat on top space plus space 2 space straight k with hat on top comma space space space space straight b with rightwards arrow on top space equals space straight i with hat on top space minus space straight j with hat on top space minus space 3 space straight k with hat on top comma space space space straight c with rightwards arrow on top space equals space 4 space straight i with hat on top space minus space 3 space straight j with hat on top space plus space straight k with hat on top
    Now,       BC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight B space equals space straight c with rightwards arrow on top space minus space straight b with rightwards arrow on top space equals space 3 space straight i with hat on top space minus space 2 space straight j with hat on top space plus space 4 space straight k with hat on top
                  BA with rightwards arrow on top space equals space straight P. straight V. space of space straight A space minus space straight P. straight V. space of space straight B space equals space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space equals 2 space straight i with hat on top space plus space 5 space straight k with hat on top
    therefore space space space BC with rightwards arrow on top cross times BA with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 3 cell negative 2 end cell 4 row 2 0 5 end table close vertical bar space equals space straight i with hat on top space open vertical bar table row cell negative 2 end cell 4 row cell space space space 0 end cell 5 end table close vertical bar space minus straight j with hat on top space open vertical bar table row 3 4 row 2 5 end table close vertical bar plus straight k with hat on top space open vertical bar table row 3 cell negative 2 end cell row 2 cell space space space 0 end cell end table close vertical bar
space space space space space space space space space space space space space space space space space space space space space space space equals space left parenthesis negative 10 minus 0 right parenthesis space straight i with hat on top space minus space left parenthesis 15 minus 8 right parenthesis space straight j with hat on top space plus space left parenthesis 0 plus 4 right parenthesis space straight k with hat on top space equals space minus 10 space straight i with hat on top space minus space 7 space straight j with hat on top space plus space 4 space straight k with hat on top
open vertical bar BC with rightwards arrow on top space cross times space BA with rightwards arrow on top close vertical bar space equals space square root of 100 plus 49 plus 16 end root space equals space square root of 165
Area space of space increment ABC space equals space 1 half space open vertical bar BC with rightwards arrow on top space cross times space BA with rightwards arrow on top space space close vertical bar space equals space 1 half square root of 165 space sq. space units
    Question 522
    CBSEENMA12034229
    Question 523
    CBSEENMA12034230

    Prove that the points A, B and C with position vectors straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top, respectively are collinear if and only if straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top space plus space straight c with rightwards arrow on top space cross times space straight a with rightwards arrow on top space plus space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space 0 with rightwards arrow on top.

    Solution
    straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top are position vectors of A, B, C respectively.
    therefore space space space BC with rightwards arrow on top space equals straight P. straight V. space of space straight C space minus space straight P. straight V. space of thin space straight B space equals space straight c with rightwards arrow on top space minus space straight b with rightwards arrow on top
    and CA with rightwards arrow on top space equals space straight P. straight V. space of space straight A space minus space straight P. straight V. space of space straight C space equals space straight a with rightwards arrow on top space minus space straight c with rightwards arrow on top
    Points A, B, C are collinear.
                      iff    BC with rightwards arrow on top space cross times space CA with rightwards arrow on top space equals space 0
     i.e.,           iff  left parenthesis straight c with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis space cross times space left parenthesis straight a with rightwards arrow on top space minus straight c with rightwards arrow on top right parenthesis space equals space 0
    i.e.,            iff straight c with rightwards arrow on top cross times straight a with rightwards arrow on top space minus space straight c with rightwards arrow on top cross times space straight c with rightwards arrow on top minus straight b with rightwards arrow on top cross times straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top
    i.e.,           iff straight c with rightwards arrow on top cross times straight a with rightwards arrow on top space minus space 0 with rightwards arrow on top space plus straight a with rightwards arrow on top space cross times straight b with rightwards arrow on top space plus space straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top space space space space space space space space space space space open square brackets because space space straight c with rightwards arrow on top space cross times space straight c with rightwards arrow on top space equals space 0 comma space space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space minus straight b with rightwards arrow on top space cross times space straight a with rightwards arrow on top close square brackets
    i.e.,           iff straight a with rightwards arrow on top cross times straight b with rightwards arrow on top plus straight b with rightwards arrow on top cross times straight c with rightwards arrow on top plus straight c with rightwards arrow on top cross times straight a with rightwards arrow on top space equals space 0 with rightwards arrow on top

    Question 524
    CBSEENMA12034231

    If straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top are the position vectors of the non-collinear points A, B, C respectively in space, show that straight b with rightwards arrow on top cross times straight c with rightwards arrow on top space plus space straight c with rightwards arrow on top space cross times straight a with rightwards arrow on top space plus space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top is perpendicular to plane ABC.

    Solution

    We have,
                  AB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A space equals space straight b with rightwards arrow on top minus straight a with rightwards arrow on top
AC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight A space equals space straight c with rightwards arrow on top space minus space straight a with rightwards arrow on top
    Vector perpendicular to plane ABC
                              = Vector perpendicular to AB with rightwards arrow on top space and space AC with rightwards arrow on top
                              equals space AB with rightwards arrow on top cross times AC with rightwards arrow on top space equals space left parenthesis straight b with rightwards arrow on top minus straight a with rightwards arrow on top right parenthesis space cross times space left parenthesis straight c with rightwards arrow on top minus straight a with rightwards arrow on top right parenthesis
equals space straight b with rightwards arrow on top cross times straight c with rightwards arrow on top space minus straight b with rightwards arrow on top space cross times space straight a with rightwards arrow on top space minus space straight a with rightwards arrow on top space cross times space straight c with rightwards arrow on top space plus space straight a with rightwards arrow on top cross times space straight a with rightwards arrow on top space equals space straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top space plus space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top space cross times space straight a with rightwards arrow on top space plus space 0 with rightwards arrow on top
equals space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space plus space straight b with rightwards harpoon with barb upwards on top space cross times space straight c with rightwards arrow on top space plus space straight c with rightwards arrow on top space cross times space straight a with rightwards arrow on top

    Question 525
    CBSEENMA12034232

     Let A, B and C be any three non-collinear points with position vectors straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top respectively. Show that the perpendicular distance from C to the straight line through A and B is fraction numerator open vertical bar straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top space plus space straight c with rightwards arrow on top space cross times space straight a with rightwards arrow on top space plus space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar over denominator open vertical bar straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top close vertical bar end fraction.

    Solution

    Let straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top be position vectors of A, B, C respectively.
    From C, draw CL space perpendicular space AB.
    AB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A space equals space straight b with rightwards arrow on top minus straight a with rightwards arrow on top
AC with rightwards arrow on top space equals space straight P. straight V. space of space straight C space minus space straight P. straight V. space of space straight A space equals straight c with rightwards arrow on top space minus space straight a with rightwards arrow on top
    In rt. angle straight d   increment ALC comma
                    CL over AC space equals sin space straight A
    therefore space space space space CL space equals space AC space sin space straight A

                      equals space fraction numerator left parenthesis AC right parenthesis thin space left parenthesis AB right parenthesis space sin space straight A over denominator AB end fraction space equals space fraction numerator open vertical bar AC with rightwards arrow on top cross times space AB with rightwards arrow on top close vertical bar over denominator open vertical bar AB with rightwards arrow on top close vertical bar end fraction space equals space fraction numerator open vertical bar left parenthesis straight c with rightwards arrow on top space minus straight a with rightwards arrow on top right parenthesis space cross times left parenthesis straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top right parenthesis close vertical bar over denominator open vertical bar straight b with rightwards arrow on top minus straight a with rightwards arrow on top close vertical bar end fraction
equals space fraction numerator open vertical bar straight c with rightwards arrow on top space cross times space straight b with rightwards arrow on top space minus space straight c with rightwards arrow on top cross times space stack straight a space with rightwards arrow on top space minus space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar over denominator open vertical bar straight b with rightwards arrow on top minus space straight a with rightwards arrow on top close vertical bar end fraction space equals space fraction numerator open vertical bar negative straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top space minus space straight c with rightwards arrow on top space cross times straight a with rightwards arrow on top space minus space straight a with rightwards arrow on top cross times space straight b with rightwards arrow on top space plus space 0 with rightwards arrow on top close vertical bar over denominator open vertical bar straight b with rightwards arrow on top space minus straight a with rightwards arrow on top close vertical bar end fraction
therefore space space space required space distance space equals space fraction numerator open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space plus space straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top space plus space straight c with rightwards arrow on top space cross times space straight a with rightwards arrow on top close vertical bar over denominator open vertical bar straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top close vertical bar end fraction.

    Question 526
    CBSEENMA12034234

    If straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top be any three vectors, then straight a with rightwards arrow on top cross times space open parentheses straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top close parentheses space space equals space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top space cross times space straight c with rightwards arrow on top.

    Solution

    Let straight a with rightwards arrow on top space equals space straight a subscript 1 straight i with hat on top space plus straight a subscript 2 straight j with hat on top space plus space straight a subscript 3 straight k with hat on top comma space space straight b with rightwards arrow on top space equals space straight b subscript 1 straight i with hat on top space plus space straight b subscript 2 straight j with hat on top space plus space straight b subscript 3 straight k with hat on top comma space straight c with rightwards arrow on top space equals straight c subscript 1 straight i with hat on top space plus space straight c subscript 2 straight j with hat on top space plus space straight c subscript 3 straight k with hat on top
    L.H.S. = straight a with rightwards arrow on top space cross times space left parenthesis straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top right parenthesis
                equals space left parenthesis straight a subscript 1 straight i with hat on top space plus space straight a subscript 2 straight j with hat on top space plus space straight a subscript 3 straight k with hat on top right parenthesis space cross times space open curly brackets left parenthesis straight b subscript 1 space plus space straight c subscript 1 right parenthesis space straight i with hat on top space plus left parenthesis straight b subscript 2 plus straight c subscript 2 right parenthesis space straight j with hat on top space plus left parenthesis straight b subscript 3 plus straight c subscript 3 right parenthesis space straight k with hat on top close curly brackets
equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row cell straight a subscript 1 end cell cell straight a subscript 2 end cell cell straight a subscript 3 end cell row cell straight b subscript 1 plus straight c subscript 1 end cell cell straight b subscript 2 plus straight c subscript 2 end cell cell straight b subscript 3 plus straight c subscript 3 end cell end table close vertical bar space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row cell straight a subscript 1 end cell cell straight a subscript 2 end cell cell straight a subscript 3 end cell row cell straight b subscript 1 end cell cell straight b subscript 2 end cell cell straight b subscript 3 end cell end table close vertical bar plus space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row cell straight a subscript 1 end cell cell straight a subscript 2 end cell cell straight a subscript 3 end cell row cell straight c subscript 1 end cell cell straight b subscript 2 end cell cell straight b subscript 3 end cell end table close vertical bar
space equals straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top space cross times space straight c with rightwards arrow on top space equals space straight R. straight H. straight S.

    Question 527
    CBSEENMA12034235

    Prove that straight a with rightwards arrow on top space cross times space left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space plus space straight b with rightwards arrow on top space cross times space left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space plus space straight c with rightwards arrow on top space cross times space left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis space space equals space 0

    Solution

    L.H.S. = straight a with rightwards arrow on top cross times left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space plus space straight b with rightwards arrow on top space cross times space left parenthesis straight c with rightwards arrow on top space plus space straight a with rightwards arrow on top right parenthesis space plus space space straight c with rightwards arrow on top left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis
                equals space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top space cross times space straight c with rightwards arrow on top space plus space straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top space plus space straight b with rightwards arrow on top space cross times space straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top space cross times space straight a with rightwards arrow on top space plus space straight c with rightwards arrow on top space cross times space straight b with rightwards arrow on top
equals space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top space cross times space straight c with rightwards arrow on top space plus space straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top space minus space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top space cross times space straight c with rightwards arrow on top space minus space straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top space equals space straight R. straight H. straight S.

    Question 528
    CBSEENMA12034237

    Given that straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0 space space and space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space 0 with rightwards arrow on top. what can you conclude about the vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top?

    Solution

    We have
                             straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0                                              ...(1)
    and                  straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space 0 with rightwards arrow on top                                            ...(2)
    From (1), it is clear that
     either                         straight a with rightwards arrow on top space equals space 0 with rightwards arrow on top space space or space space straight b with rightwards arrow on top space equals space 0 with rightwards arrow on top space space space or space space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space are space perpendicular.
         From (2), it is clear that
         either    straight a with rightwards arrow on top space equals space 0 space space space space space or space space space straight b with rightwards arrow on top space equals space 0 with rightwards arrow on top space space space or space space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space space are space parallel.
        Now,    straight a with rightwards arrow on top comma space straight b with rightwards arrow on top are perpendicular and straight a with rightwards arrow on top space straight b with rightwards arrow on top are parallel cannot hold simultaneously.
    therefore either straight a with rightwards arrow on top space equals 0 with rightwards arrow on top space space space or space space straight b with rightwards arrow on top space equals 0 with rightwards arrow on top.

    Question 529
    CBSEENMA12034238

    If either straight a with rightwards arrow on top space equals space 0 with rightwards arrow on top space space space or space space straight b with rightwards arrow on top space equals space 0 with rightwards arrow on top comma space then space space space space straight a with rightwards arrow on top cross times space straight b with rightwards arrow on top space equals space 0 with rightwards arrow on top. Is the  converse true? Justify your answer with an example.

    Solution

    If straight a with rightwards arrow on top space equals space 0 with rightwards arrow on top space space or space space straight b with rightwards arrow on top space equals space 0 with rightwards arrow on top space then space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals 0 with rightwards arrow on top.
    But the converse is not true, i.e., if straight a with rightwards arrow on top cross times straight b with rightwards arrow on top space equals space 0 with rightwards arrow on top then straight a with rightwards arrow on top space equals space 0 with rightwards arrow on top space space or space space straight b with rightwards arrow on top space equals space 0 with rightwards arrow on top may not hold.
            For example, consider the vectors straight a with rightwards arrow on top space equals space straight i with hat on top comma space space straight b with rightwards arrow on top space equals straight i with hat on top space.
                              Then straight a with rightwards arrow on top space not equal to space 0 with rightwards arrow on top also,    straight b with rightwards arrow on top space not equal to space 0 with rightwards arrow on top    but straight a with rightwards arrow on top cross times straight b with rightwards arrow on top space equals space straight i with hat on top space cross times space straight i with hat on top space equals space 0 with rightwards arrow on top.

    Question 530
    CBSEENMA12034241

    If   straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top comma space show that straight a with rightwards arrow on top cross times straight b with rightwards arrow on top space equals space straight b with rightwards arrow on top cross times straight c with rightwards arrow on top space equals straight c with rightwards arrow on top cross times straight a with rightwards arrow on top. Interpret the result geometrically.

    Solution

    Now, straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top space space space space space space space space space space space space space space space space rightwards double arrow space space space space straight a with rightwards arrow on top plus straight b with rightwards arrow on top space equals space minus straight c with rightwards arrow on top space space space space rightwards double arrow space space space straight a with rightwards arrow on top space cross times left parenthesis straight a with rightwards arrow on top cross times straight b with rightwards arrow on top right parenthesis space equals space minus straight a with rightwards arrow on top space cross times space straight c with rightwards arrow on top
    rightwards double arrow space space space space straight a with rightwards arrow on top cross times straight a with rightwards arrow on top plus straight a with rightwards arrow on top cross times straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top cross times straight a with rightwards arrow on top space space rightwards double arrow space space space 0 with rightwards arrow on top plus straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top space cross times space straight a with rightwards arrow on top space space space space space rightwards double arrow space space straight a with rightwards arrow on top cross times straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top space cross times space straight a with rightwards arrow on top
                                                                                                                                     ...(1)
    Similarly,   straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top                                                                                  ...(2)
    From (1) and (2), we get, 
    straight a with rightwards arrow on top cross times straight b with rightwards arrow on top space equals space straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top space equals straight c with rightwards arrow on top cross times space straight a with rightwards arrow on top
    Let  straight a with rightwards arrow on top cross times straight b with rightwards arrow on top space equals space straight b with rightwards arrow on top cross times straight c with rightwards arrow on top space equals space straight c with rightwards arrow on top cross times straight a with rightwards arrow on top space equals straight p with rightwards arrow on top
    therefore space space space straight p with rightwards arrow on top space is space perpendicular space to space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space and space straight c with rightwards arrow on top
rightwards double arrow space space straight p with rightwards arrow on top space is space perpendicular space to space the space plane space of space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top
rightwards double arrow space space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top space are space coplanar.

    Question 531
    CBSEENMA12034243
    Question 532
    CBSEENMA12034244
    Question 533
    CBSEENMA12034246

    If straight a with rightwards arrow on top not equal to 0 with rightwards arrow on top comma space space do comma space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space straight a with rightwards arrow on top. space straight c with rightwards arrow on top space and space space straight a with rightwards arrow on top space cross times straight b with rightwards arrow on top space equals straight a with rightwards arrow on top space cross times space straight c with rightwards arrow on top space together space imply space straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top ?

    Solution

    We have,    straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space straight a with rightwards arrow on top. space straight c with rightwards arrow on top
         therefore space space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top. space straight c with rightwards arrow on top space equals space 0 space space space space rightwards double arrow space space space space straight a with rightwards arrow on top. space left parenthesis straight b with rightwards arrow on top space minus space straight c with rightwards arrow on top right parenthesis space equals space 0
therefore space space space space there space are space three space possibilities colon
    (i) straight a with rightwards arrow on top space equals space 0 degree           left parenthesis ii right parenthesis space straight b with rightwards arrow on top space minus space straight c with rightwards arrow on top space equals 0 with rightwards arrow on top                (iii) straight a with rightwards arrow on top is perpendicular to straight b with rightwards arrow on top space minus space straight c with rightwards arrow on top
    Again,              straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space straight a with rightwards arrow on top space cross times space straight c with rightwards arrow on top
    therefore space space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top space cross times straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top space space space space space rightwards double arrow space space straight a with rightwards arrow on top space cross times space left parenthesis straight b with rightwards arrow on top minus straight c with rightwards arrow on top right parenthesis space equals space 0 with rightwards arrow on top
therefore space space space again space there space are space three space possibilities colon
left parenthesis straight i right parenthesis space space straight a with rightwards arrow on top space equals space 0 with rightwards arrow on top comma space space space left parenthesis ii right parenthesis space straight b with rightwards arrow on top space minus space straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top comma space space space left parenthesis iii right parenthesis space straight a with rightwards arrow on top space is space parallel space to space straight b with rightwards arrow on top space minus space straight c with rightwards arrow on top
Now comma space straight a with rightwards arrow on top space is space given space to space be space non minus zero space vector
therefore space space space space we space have space the space following space possibilities space left colon
left parenthesis 1 right parenthesis space straight b with rightwards arrow on top space minus space straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top
left parenthesis 2 right parenthesis space straight a with rightwards arrow on top space is space perpendicular space to space straight b with rightwards arrow on top minus straight c with rightwards arrow on top space space and space straight a with rightwards arrow on top space is space parllel space to space straight b with rightwards arrow on top minus straight c with rightwards arrow on top comma space which space is space absurd.
therefore space space space space space space only space possibility space left space is space straight b with rightwards arrow on top minus straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top space space or space space straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top.

space space space space

    Question 534
    CBSEENMA12034248

    If straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space straight a with rightwards arrow on top space cross times space straight c with rightwards arrow on top and straight a with rightwards arrow on top not equal to 0 with rightwards arrow on top comma space then straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top space plus space straight lambda space straight alpha with rightwards arrow on top comma space where space straight lambda space is space straight a space scalar.

    Solution
    straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space straight a with rightwards arrow on top space cross times space straight c with rightwards arrow on top space space space rightwards double arrow space space space space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top space cross times space straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top
    rightwards double arrow space space space straight a with rightwards arrow on top space cross times space left parenthesis straight b with rightwards arrow on top space minus space straight c with rightwards arrow on top right parenthesis space equals space 0 with rightwards arrow on top space space space rightwards double arrow space space space straight b with rightwards arrow on top minus straight c with rightwards arrow on top space is space parallel space to space straight a with rightwards arrow on top
rightwards double arrow space space space space straight b with rightwards arrow on top space minus space straight c with rightwards arrow on top space equals space straight lambda space straight a with rightwards arrow on top space space space space space rightwards double arrow space space space straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top space plus space straight lambda space straight a with rightwards arrow on top comma space where space straight lambda space space is space scalar
    Question 535
    CBSEENMA12034250

    If straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top  are mutually perpendicular unit vectors and straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top comma then straight b with rightwards arrow on top space equals straight c with rightwards arrow on top space cross times straight a with rightwards arrow on top space and space straight a with rightwards arrow on top space equals space straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top.

    Solution

    Since,  straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top are mutually perpendicular  unit vectors
    therefore space space space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 1 comma space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight c with rightwards arrow on top close vertical bar space equals space 1
and space space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space straight b with rightwards arrow on top. space straight c with rightwards arrow on top space equals space straight c with rightwards arrow on top. space straight a with rightwards arrow on top space equals space 0
Also comma space space space space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top
therefore space space space space straight c with rightwards arrow on top space is space perpendicular space to space the space plane space of space straight a with rightwards arrow on top space and space straight b with rightwards arrow on top
therefore space space space space straight b with rightwards arrow on top space is space perpendicular space to space the space plane space of space straight c with rightwards arrow on top space and space straight a with rightwards arrow on top comma
space space space space space space space space space straight a with rightwards arrow on top space is space perpendicular space to space the space plane space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top
therefore space space straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top space cross times space straight a with rightwards arrow on top space. space straight a with rightwards arrow on top space equals space straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top.

    Question 536
    CBSEENMA12034253

    If straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top space cross times space straight d with rightwards arrow on top space and space straight a with rightwards arrow on top space cross times space straight c with rightwards arrow on top space equals space straight b with rightwards arrow on top space cross times space straight d with rightwards arrow on top comma space show space that space straight a with rightwards arrow on top space minus space straight d with rightwards arrow on top is parallel to straight b with rightwards arrow on top minus straight c with rightwards arrow on top space provided space straight a with rightwards arrow on top space not equal to space straight d with rightwards arrow on top space and space straight b with rightwards arrow on top not equal to straight c with rightwards arrow on top.

    Solution
    open table attributes columnalign right end attributes row cell We space have space straight a with rightwards arrow on top cross times straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top space cross times space straight d with rightwards arrow on top end cell row cell and space straight a with rightwards arrow on top cross times space straight c with rightwards arrow on top space equals straight b with rightwards arrow on top space cross times space straight d with rightwards arrow on top end cell end table close curly brackets space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
    straight a with rightwards arrow on top space minus space straight d with rightwards arrow on top will be parallel to straight b with rightwards arrow on top minus straight c with rightwards arrow on top

    if left parenthesis straight a with rightwards arrow on top space minus space straight d with rightwards arrow on top right parenthesis space cross times space left parenthesis straight b with rightwards arrow on top minus straight c with rightwards arrow on top right parenthesis space equals space 0 with rightwards arrow on top space space space straight i. straight e. comma space if space straight a with rightwards arrow on top space cross times straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top space cross times space straight c with rightwards arrow on top space minus space straight d with rightwards arrow on top space cross times space straight b with rightwards arrow on top space plus space straight d with rightwards arrow on top space cross times space straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top
    straight i. straight e. comma space if space left parenthesis straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space plus space straight d with rightwards arrow on top space cross times space straight c with rightwards arrow on top right parenthesis space minus space left parenthesis straight a with rightwards arrow on top space cross times space straight c with rightwards arrow on top space plus space straight d with rightwards arrow on top space cross times space straight b with rightwards arrow on top right parenthesis space equals space 0 with rightwards arrow on top
straight i. straight e. comma space if space left parenthesis straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space minus space straight c with rightwards arrow on top space cross times space straight d with rightwards arrow on top right parenthesis space minus space left parenthesis straight a with rightwards arrow on top space cross times space straight c with rightwards arrow on top space minus straight b with rightwards arrow on top space cross times space straight d with rightwards arrow on top right parenthesis space equals space 0 with rightwards arrow on top
straight i. straight e. comma space if space 0 with rightwards arrow on top space minus space 0 with rightwards arrow on top space equals space 0 with rightwards arrow on top space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
straight i. straight e. comma space if space 0 with rightwards arrow on top space equals space 0 with rightwards arrow on top space which space is space true.
    Hence the result. 
    Question 537
    CBSEENMA12034255

    Show that left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space cross times space left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis space equals space 2 space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top .
    OR
    Show that left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space cross times space left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis space equals space 2 space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top and give a geometrical interpretation of it.

    Solution

    L.H.S. = left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space cross times space left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis space equals space straight a with rightwards arrow on top space cross times space straight a with rightwards arrow on top space plus space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space minus space straight b with rightwards arrow on top space cross times space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top space cross times space straight b with rightwards arrow on top
                equals space straight a with rightwards arrow on top space cross times space straight a with rightwards arrow on top space plus space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space minus space straight b with rightwards arrow on top space equals space 0 space plus space 2 straight a with rightwards arrow on top cross times straight b with rightwards arrow on top space minus space 0 with rightwards arrow on top space equals space 2 space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top
equals space straight R. straight H. straight S.
    Gemetrical Interpretation
    Let O be the point of intersection of diagonals AC and BD of || gm ABCD.
               Let  AO with rightwards arrow on top space equals straight a with rightwards arrow on top comma space space OD with rightwards arrow on top space equals space straight b with rightwards arrow on top
    therefore space space space space space OB with rightwards arrow on top space equals space minus straight b with rightwards arrow on top
    therefore space space space AB with rightwards arrow on top space equals space AO with rightwards arrow on top space plus space OB with rightwards arrow on top space equals space straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top
           AD with rightwards arrow on top space equals AO with rightwards arrow on top space plus space OD with rightwards arrow on top space equals straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top

    therefore space space space left parenthesis straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top right parenthesis space cross times space left parenthesis straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis space equals space vector space area space of space vertical line vertical line space gm space ABCD
Also comma space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space vector space area space of space vertical line vertical line space gm space whose space sides space area space straight a with rightwards arrow on top space space and space straight b with rightwards arrow on top.
    therefore space space space space left parenthesis straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis space cross times space left parenthesis straight a with rightwards arrow on top space plus straight b with rightwards arrow on top right parenthesis space equals space 2 space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top implies that the area of || gm ABCD is twice the area of the || gm whose adjacent sides are semi-diagonals of the first parallelogram.

    Question 538
    CBSEENMA12034259

    If straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top are three vectors such that straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top comma space space space straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top space equals space straight a with rightwards arrow on top comma space show that the three vectors straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top are orthogonal in pairs and open vertical bar straight a with rightwards arrow on top close vertical bar space equals space open vertical bar straight c with rightwards arrow on top close vertical bar comma space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals 1.

    Solution
    because space space space space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top
therefore space space straight c with rightwards arrow on top space is space vector space which space is space perpendicular space to space straight a with rightwards arrow on top space as space well space as space straight b with rightwards arrow on top.
Again comma space straight b with rightwards arrow on top space cross times straight c with rightwards arrow on top space equals space straight a with rightwards arrow on top
therefore space space space straight a with rightwards arrow on top space is space perpendicular space to space straight b with rightwards arrow on top space as space well space as space straight c with rightwards arrow on top.
therefore space space space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top space are space mutually space orthogonal
Again comma space space space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top
rightwards double arrow space space space space space space open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight c with rightwards arrow on top close vertical bar
rightwards double arrow space space space space space open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight c with rightwards arrow on top close vertical bar space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space
                                                                                     open square brackets because space space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space are space perpendicular close square brackets
    Again,  straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top space equals space straight a with rightwards arrow on top
    rightwards double arrow space space space space space open vertical bar straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top close vertical bar space equals straight a with rightwards arrow on top                          rightwards double arrow space space space space space space space space space space open vertical bar straight b with rightwards arrow on top close vertical bar space space open vertical bar straight c with rightwards arrow on top close vertical bar space equals space open vertical bar straight a with rightwards arrow on top close vertical bar                 ...(2)
                                                                                       open square brackets because space space straight b with rightwards arrow on top comma space space straight c with rightwards arrow on top space are space perpendicular close square brackets
    From (1) and (2),
                          open vertical bar straight b with rightwards arrow on top close vertical bar space open vertical bar straight c with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight c with rightwards arrow on top close vertical bar space space space space space space space rightwards double arrow space space open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space 1 space space space space space space space space space space space rightwards double arrow space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 1
    therefore space space space space from space left parenthesis 1 right parenthesis comma space space space open vertical bar straight a with rightwards arrow on top close vertical bar space equals space open vertical bar straight c with rightwards arrow on top close vertical bar
                                                                       
                                                              
    Question 539
    CBSEENMA12034260

    If straight a with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top space and straight b with rightwards arrow on top space equals space straight j with hat on top space minus space straight k with hat on top.  Find a vector straight c with rightwards arrow on top such that straight a with rightwards arrow on top cross times space straight c with rightwards arrow on top space equals space straight b with rightwards arrow on top and straight a with rightwards arrow on top. space straight c with rightwards arrow on top space equals space 3.

    Solution

    Here ,    straight a with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top comma space space space straight b with rightwards arrow on top space equals space straight j with hat on top space minus space straight k with hat on top
    Let     straight c with rightwards arrow on top space equals space straight x space straight i with hat on top space plus space straight y space straight j with hat on top space plus space straight z space straight k with hat on top
    Now,              straight a with rightwards arrow on top space cross times space straight c with rightwards arrow on top space equals space straight b with rightwards arrow on top
    space rightwards double arrow space space space space space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 1 1 1 row straight x straight y straight z end table close vertical bar space equals straight j with hat on top space minus space straight k with hat on top
space rightwards double arrow space space space space straight i with hat on top space open vertical bar table row 1 1 row straight y straight z end table close vertical bar space minus space straight j with hat on top space open vertical bar table row 1 1 row straight x straight z end table close vertical bar space plus space straight k with hat on top space open vertical bar table row 1 1 row straight x straight y end table close vertical bar space equals space straight j with hat on top space minus space straight k with hat on top
space rightwards double arrow space space left parenthesis straight z minus straight y right parenthesis space straight i with hat on top space minus space left parenthesis straight z minus straight x right parenthesis space straight j with hat on top space space plus space left parenthesis straight y minus straight x right parenthesis space straight k with hat on top space equals space straight j with hat on top space minus space straight k with hat on top space space space space
    rightwards double arrow space space space space space space straight z minus straight y space equals space 0                                                         ...(1)
               x - z = 1                                                            ...(2)
                x - y = 1                                                           ...(3)
    Also,     straight a with rightwards arrow on top. space straight c with rightwards arrow on top space equals 3 space space space space space space space space space space space space space space space space space rightwards double arrow space space space left parenthesis 1 right parenthesis thin space left parenthesis straight x right parenthesis space plus space left parenthesis 1 right parenthesis thin space left parenthesis straight y right parenthesis space plus space left parenthesis 1 right parenthesis space left parenthesis straight z right parenthesis space equals space 3
    therefore space space space space space space straight x plus straight y plus straight z space equals space 3                                                    ...(4)
    From (1),    y = z
    therefore    from (4), we get,
                           straight x plus 2 space straight y space equals space 3                                          ...(5)
    Subtracting (3) from (5), we get,
                       3 straight y space equals space 2 space space space space or space space space straight y space equals space 2 over 3 space equals space straight z
    therefore space space space from space left parenthesis 5 right parenthesis comma space space space straight x plus 4 over 3 space equals space 3 space space space space space rightwards double arrow space space space space straight x space equals space 3 space minus space 4 over 3 space equals space 5 over 3
therefore space space space we space have space straight x space equals space 5 over 3 comma space space space straight y space equals space space 2 over 3 comma space space space straight z space equals space 2 over 3
therefore space space space straight c with rightwards arrow on top space equals space 5 over 3 straight i with hat on top space space plus space 2 over 3 straight j with hat on top space plus space 2 over 3 straight k with hat on top

    Question 540
    CBSEENMA12034261

    Let straight a with rightwards arrow on top space equals straight i with hat on top space plus space 4 space straight j with hat on top space plus space 2 space straight k with hat on top comma space space space space space straight b with rightwards arrow on top space equals space 3 space straight i with hat on top space minus space 2 space straight j with hat on top space plus space space 7 space straight k with hat on top and straight c with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space straight j with hat on top space plus space 4 space straight k with hat on top. Find a vector straight d with rightwards arrow on top which is perpendicular to both straight a with rightwards arrow on top space and space straight b with rightwards arrow on top comma space space straight c with rightwards arrow on top. space straight d with rightwards arrow on top space equals space 15.

    Solution
    straight a with rightwards arrow on top space equals space straight i with hat on top space plus space 4 space straight j with hat on top space plus space 2 space straight k with hat on top comma space space space space space straight b with rightwards arrow on top space equals space 3 space straight i with hat on top space minus space 2 space straight j with hat on top space plus space space 7 space straight k with hat on top comma space space straight c with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space straight j with hat on top space plus space 4 space straight k with hat on top
       therefore space space space space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 1 4 2 row 3 cell negative 2 end cell 7 end table close vertical bar space equals space straight i with hat on top space open vertical bar table row cell space space space 4 end cell 2 row cell negative 2 end cell 7 end table close vertical bar space minus space straight j with hat on top space open vertical bar table row 1 2 row 3 7 end table close vertical bar plus space straight k with hat on top space open vertical bar table row 1 4 row 3 cell negative 2 end cell end table close vertical bar
space space space space space space space space space space space space space space space space space space space space space equals space left parenthesis 28 plus 4 right parenthesis space straight i with hat on top space minus space left parenthesis 7 minus 6 right parenthesis space straight j with hat on top plus space left parenthesis negative 2 minus 12 right parenthesis space straight k with hat on top
space space space space space space space space space space space space space space space space space space space space space space equals space 32 space straight i with hat on top space minus space straight j with hat on top space minus space 14 space straight k with hat on top
    which is a vector perpendicular to straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.
    Since straight d with rightwards arrow on top is perpendicular to both straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.
    therefore space space space space straight d with rightwards arrow on top space space is space parallel space to space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top.
therefore space space space space space space space space space space space space space space straight d with rightwards arrow on top space equals space straight lambda left parenthesis straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top right parenthesis comma space space where space straight lambda space is space scalar space to space be space determined.
therefore space space space space space space space space space space space space space space straight d with rightwards arrow on top space equals space straight lambda left parenthesis 32 straight i with hat on top space minus space straight j with hat on top space minus 14 space straight k with hat on top right parenthesis
Now comma space space space straight c with rightwards arrow on top. space straight d with rightwards arrow on top space equals space 15
rightwards double arrow space space space space 2 space left parenthesis 32 space straight lambda right parenthesis space plus space left parenthesis negative 1 right parenthesis thin space left parenthesis negative straight lambda right parenthesis space plus space left parenthesis 4 right parenthesis thin space left parenthesis negative 14 space straight lambda right parenthesis space equals space 15
rightwards double arrow space space space space 64 space straight lambda space plus space straight lambda space minus space 56 space straight lambda space equals space 15 space space space space space rightwards double arrow space space space 9 space straight lambda space equals space 15 space space space space rightwards double arrow space space space space straight lambda space equals space 15 over 9 space equals 5 over 3
therefore space space space space space space space space space space space space straight d with rightwards arrow on top space equals space 5 over 3 left parenthesis 32 space straight i with hat on top space minus space straight j with hat on top space minus space 14 space straight k with hat on top right parenthesis
    Question 541
    CBSEENMA12034262

    If with reference to a right handed system of mutually perpendicular unit vector unit vector straight i with hat on top comma space straight j with hat on top comma space straight k with hat on top

    express straight beta with rightwards arrow on top in the form straight beta with rightwards arrow on top in the form straight beta with rightwards arrow on top space equals space straight beta with rightwards arrow on top subscript 1 space equals space straight beta with rightwards arrow on top subscript 1 space plus space straight beta with rightwards arrow on top subscript 2 space end subscript space where space stack straight beta subscript 1 with rightwards arrow on top space is space parallel space to space straight alpha space and space stack straight beta subscript 2 with rightwards arrow on top space is space perpendicular space to space straight alpha with rightwards arrow on top.

    Solution

    Let straight alpha with rightwards arrow on top space equals space 3 space straight i with hat on top space minus space straight j with hat on top comma space space space space straight beta with rightwards arrow on top space equals space 2 straight i with hat on top plus straight j with hat on top space minus space 3 straight k with hat on top
    Let  stack straight beta subscript 1 with rightwards arrow on top space equals space straight a subscript 1 straight i with hat on top space plus space straight a subscript 2 straight j with hat on top space plus space straight a subscript 3 straight k with hat on top comma space space stack straight beta subscript 2 with rightwards arrow on top space equals space straight b subscript 1 straight i with hat on top space plus space straight b subscript 2 straight j with hat on top space plus space straight b subscript 3 straight k with hat on top
    therefore space space space space space straight beta with rightwards arrow on top space equals straight beta with rightwards arrow on top subscript 1 plus space stack straight beta subscript 2 with rightwards arrow on top space equals space left parenthesis straight a subscript 1 plus straight b subscript 1 right parenthesis space straight i with hat on top space plus space left parenthesis straight a subscript 2 plus straight b subscript 2 right parenthesis straight j with hat on top space plus space left parenthesis straight a subscript 3 plus straight b subscript 3 right parenthesis straight k with hat on top
rightwards double arrow space space 2 straight i with hat on top space plus space straight j with hat on top space minus space 3 space straight k with hat on top space equals space left parenthesis straight a subscript 1 plus straight b subscript 1 right parenthesis straight i with hat on top space plus space left parenthesis straight a subscript 2 plus straight b subscript 2 right parenthesis space straight j with hat on top space plus space left parenthesis straight a subscript 3 plus straight b subscript 3 right parenthesis space straight k with hat on top
rightwards double arrow space space space straight a subscript 1 plus straight b subscript 1 space equals space 2 comma space space space space space straight a subscript 2 plus straight b subscript 2 space equals space 1 comma space space straight a subscript 3 plus straight b subscript 3 space equals space minus 3
therefore space space space space space space straight b subscript 1 space equals space 2 space minus straight a subscript 1 comma space space space space space straight b subscript 2 space equals space 1 minus straight a subscript 2 comma space space space straight b subscript 3 space equals space minus 3 minus straight a subscript 3 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis space space space space space space space end subscript
    Since stack straight beta subscript 1 with rightwards arrow on top is parallel to straight alpha with rightwards arrow on top
     therefore space space space space space space straight beta with rightwards arrow on top subscript 1 space cross times space straight alpha with rightwards arrow on top space equals space 0 space space space space space space rightwards double arrow space space space space space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row cell straight a subscript 1 end cell cell straight a subscript 2 end cell cell straight a subscript 3 end cell row 3 cell negative 1 end cell 0 end table close vertical bar space equals space 0 with rightwards arrow on top
rightwards double arrow space space space space space space straight a subscript 3 straight i with hat on top space plus space 3 space straight a subscript 3 straight j with hat on top space plus left parenthesis negative straight a subscript 1 space minus space 3 space straight a subscript 2 right parenthesis space straight k with hat on top space equals space 0 with rightwards arrow on top
rightwards double arrow space space space space space space straight a subscript 3 space equals space 0 comma space space space space 3 space straight a subscript 3 space equals space 0 comma space space space space space minus straight a subscript 1 space minus space 3 space straight a subscript 2 space equals space 0
rightwards double arrow space space space space space straight a subscript 3 space equals space 0 space space space straight a subscript 1 space equals space minus 3 space straight a subscript 2 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis
Again comma space space stack straight beta subscript 2 with rightwards arrow on top space is space perpendicular space to space straight alpha with rightwards arrow on top
therefore space space space space space stack straight beta subscript 2 with rightwards arrow on top space. space straight alpha with rightwards arrow on top space equals space 0 space space space space space space rightwards double arrow space space space space left parenthesis straight b subscript 1 straight i with hat on top space plus space straight b subscript 2 straight j with hat on top space plus space straight b subscript 3 straight k with hat on top right parenthesis. space space space left parenthesis 3 space straight i with hat on top space minus space straight j with hat on top right parenthesis space equals space 0
rightwards double arrow space space space space 3 space straight b subscript 1 space minus space straight b subscript 2 space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
rightwards double arrow space 3 space left parenthesis 2 minus straight a subscript 1 right parenthesis space minus space 1 left parenthesis 1 minus straight a subscript 2 right parenthesis space equals space 0 space space space space space space rightwards double arrow space space space space space 6 minus 3 space straight a subscript 1 space minus space 1 space plus space straight a subscript 2 space equals space 0
rightwards double arrow space space space 5 minus 3 space straight a subscript 1 space plus space straight a subscript 2 space equals space 0 space space space space space space
rightwards double arrow space space space 5 plus 9 space straight a subscript 2 plus space straight a subscript 2 space space space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 2 right parenthesis close square brackets
rightwards double arrow space space space space space 10 space straight a subscript 2 space equals space minus 5 space space space space space space space space space space space space space space space space space space space space space space space space space space rightwards double arrow space space space space space space straight a subscript 2 space equals space minus 1 half space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space

space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space
    therefore space space space space space straight a subscript 1 space equals 3 over 2                                                                               open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
    therefore space space space space straight beta with rightwards arrow on top subscript 1 space equals space 3 over 2 straight i with hat on top space minus space 1 half straight j with hat on top
    From (1),   straight b subscript 1 space equals 2 minus 3 over 2 space equals space 1 half comma space space space space space space space straight b subscript 2 equals space 1 plus 1 half space equals 3 over 2 comma space space straight b subscript 3 space equals space minus 3 minus 0 space equals space minus 3
    therefore space space stack straight beta subscript 2 with rightwards arrow on top space equals space 1 half straight i with hat on top space plus space 3 over 2 straight j with hat on top space minus space 3 space straight k with hat on top.
     

    Question 542
    CBSEENMA12034263

    straight A with rightwards arrow on top comma space straight B with rightwards arrow on top comma space straight C with rightwards arrow on top are unit vectors,  Suppose that  straight A with rightwards arrow on top. space straight B with rightwards arrow on top space equals space straight A with rightwards arrow on top. space straight C with rightwards arrow on top space equals space 0 and the angle between B and C is straight pi over 6. Prove that straight A with rightwards arrow on top space equals plus-or-minus 2 space open parentheses straight B with rightwards arrow on top space cross times space straight C with rightwards arrow on top close parentheses.

    Solution

    Since  straight A with rightwards arrow on top. space straight B with rightwards arrow on top space equals space straight A with rightwards arrow on top. space straight C with rightwards arrow on top space equals 0
    therefore space space space space straight A with rightwards arrow on top space is space perpendicular space to space straight B with rightwards arrow on top space as space well space as space straight C with rightwards arrow on top
therefore space space space straight A with rightwards arrow on top space is space parallel space to space straight B with rightwards arrow on top space cross times space straight C with rightwards arrow on top
    Let straight A with rightwards arrow on top space equals space straight lambda open parentheses straight B with rightwards arrow on top space cross times space straight C with rightwards arrow on top close parentheses                                                        ...(1)
    where straight lambda is some scalar
    therefore space space space open vertical bar straight A with rightwards arrow on top close vertical bar space equals space open vertical bar straight lambda close vertical bar space space open vertical bar straight B with rightwards arrow on top space cross times space straight C with rightwards arrow on top close vertical bar space space space space space space space rightwards double arrow space space space open vertical bar straight A with rightwards arrow on top close vertical bar space equals space open vertical bar straight lambda close vertical bar space space open vertical bar straight B with rightwards arrow on top close vertical bar space open vertical bar straight C with rightwards arrow on top close vertical bar space space sin space straight pi over 6 space open vertical bar straight n with hat on top close vertical bar
    where straight n with hat on top is perpendicular to straight B with rightwards arrow on top space as space well space as space straight C with rightwards arrow on top.
    rightwards double arrow space space space space space 1 space equals space open vertical bar straight lambda close vertical bar space left parenthesis 1 right parenthesis thin space left parenthesis 1 right parenthesis space space open parentheses 1 half close parentheses space left parenthesis 1 right parenthesis space space space space space space space space space space space space space space space open square brackets because space space space straight A with rightwards arrow on top comma space straight B with rightwards arrow on top comma space straight C with rightwards arrow on top space are space unit space vectors close square brackets.
    therefore space space space space space from space left parenthesis 1 right parenthesis comma space space space we space get comma space space straight A with rightwards arrow on top space space equals plus-or-minus 2 space open parentheses straight B with rightwards arrow on top space cross times space straight C with rightwards arrow on top close parentheses

    Question 543
    CBSEENMA12034264

    Give space space space straight a with rightwards arrow on top space equals space 1 over 7 left parenthesis 2 space straight i with hat on top space plus space 3 space straight j with hat on top space plus space 6 space straight k with hat on top right parenthesis comma space space straight b with rightwards arrow on top space equals space 1 over 7 left parenthesis 3 space straight i with hat on top space minus space 6 space straight j with hat on top space plus space 2 space straight k with hat on top right parenthesis comma
space space space space space space space space space space space space space space straight c with rightwards arrow on top space equals space 1 over 7 left parenthesis 6 space straight i with hat on top space plus space 2 space straight j with hat on top space minus space 3 space straight k with hat on top right parenthesis comma
    straight i with hat on top comma space straight j with hat on top comma space straight k with hat on top being a right-handed orthogonal system of unit vectors in space. Show that straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top in another such system.

    Solution

            straight a with rightwards arrow on top space equals space 1 over 7 left parenthesis 2 straight i with hat on top space plus space 3 straight j with hat on top space plus space 6 straight k with hat on top right parenthesis space equals 2 over 7 straight i with hat on top plus 3 over 7 straight j with hat on top space plus space 6 over 7 straight k with hat on top
straight b with rightwards arrow on top space equals space 1 over 7 left parenthesis 3 straight i with hat on top space minus space 6 straight j with hat on top space plus space 2 straight k with hat on top right parenthesis space equals space 3 over 7 straight i with hat on top space minus space 6 over 7 straight j with hat on top space plus space 2 over 7 straight k with hat on top
straight c with rightwards arrow on top space equals space 1 over 7 left parenthesis 6 straight i with hat on top space plus space 2 straight j with hat on top space minus space 3 straight k with hat on top right parenthesis space equals space 6 over 7 straight i with hat on top space plus space 2 over 7 straight j with hat on top space minus space 3 over 7 straight k with hat on top
    therefore space space space space straight a space equals space square root of open parentheses 2 over 7 close parentheses squared plus open parentheses 3 over 7 close parentheses squared plus open parentheses 6 over 7 close parentheses squared end root space equals space square root of 4 over 49 plus 9 over 49 plus 36 over 49 end root space equals square root of 49 over 49 end root space equals 1
              straight b equals space square root of open parentheses 3 over 7 close parentheses squared plus open parentheses fraction numerator negative 6 over denominator 7 end fraction close parentheses squared plus open parentheses 2 over 7 close parentheses squared end root space equals space square root of 9 over 49 plus 36 over 49 plus 4 over 49 end root space equals space square root of 49 over 49 end root space equals 1
straight c space equals space square root of open parentheses 6 over 7 close parentheses squared plus open parentheses 2 over 7 close parentheses squared plus open parentheses fraction numerator negative 3 over denominator 7 end fraction close parentheses squared end root space equals square root of 36 over 49 plus 4 over 49 plus 9 over 49 end root space equals square root of 49 over 49 end root space equals space 1
    therefore space space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top space are space unit space vectors.
                    straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space open parentheses 2 over 7 close parentheses space open parentheses 3 over 7 close parentheses plus space open parentheses 3 over 7 close parentheses space open parentheses fraction numerator negative 6 over denominator 7 end fraction close parentheses space plus space open parentheses 6 over 7 close parentheses space open parentheses 2 over 7 close parentheses space equals 6 over 49 minus 18 over 49 plus 12 over 49 equals 0
straight a with rightwards arrow on top. space straight c with rightwards arrow on top space equals space open parentheses 2 over 7 close parentheses space open parentheses 6 over 7 close parentheses space plus space open parentheses 3 over 7 close parentheses space open parentheses 2 over 7 close parentheses space plus open parentheses 6 over 7 close parentheses space open parentheses fraction numerator negative 3 over denominator 7 end fraction close parentheses space equals 12 over 49 plus 6 over 49 minus 18 over 49 space equals 0
straight b with rightwards arrow on top. straight c with rightwards arrow on top space equals space open parentheses 3 over 7 close parentheses space open parentheses 6 over 7 close parentheses plus open parentheses fraction numerator negative 6 over denominator 7 end fraction close parentheses space open parentheses 2 over 7 close parentheses plus open parentheses 2 over 7 close parentheses space open parentheses fraction numerator negative 3 over denominator 7 end fraction close parentheses space equals space 18 over 49 minus 12 over 49 minus 6 over 49 equals space 0
    therefore space space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top are mutually orthogonal vectors.
    Now,  
       straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space 1 over 49 open vertical bar table row cell straight i with hat on top end cell cell space straight j with hat on top end cell cell straight k with hat on top end cell row 2 cell space space 3 end cell 6 row 3 cell negative 6 end cell 2 end table close vertical bar space equals space 1 over 49 open square brackets left parenthesis 6 plus 36 right parenthesis space straight i with hat on top space minus space left parenthesis 4 minus 18 right parenthesis space straight j with hat on top space plus space left parenthesis negative 12 minus 9 right parenthesis straight k with hat on top close square brackets
space space space space space space space space space space space space space equals space 1 over 49 left square bracket 42 straight i with hat on top space plus space 14 straight j with hat on top space minus space 21 straight k with hat on top right square bracket space equals space 1 over 7 left parenthesis 6 straight i with hat on top space plus 2 straight j with hat on top space minus 3 straight k with hat on top right parenthesis space equals space straight c with rightwards arrow on top
straight b with rightwards arrow on top space cross times space straight c with rightwards arrow on top space equals space 1 over 49 open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 3 cell negative 6 end cell 2 row 6 2 cell negative 3 end cell end table close vertical bar space equals 1 over 49 open square brackets left parenthesis 18 minus 4 right parenthesis straight i with hat on top space minus space left parenthesis negative 9 minus 12 right parenthesis space straight j with hat on top space plus space left parenthesis 6 plus 36 right parenthesis space straight k with hat on top close square brackets
space space space space space space space space space space space space space space equals space 1 over 49 left square bracket 14 space straight i with hat on top space plus 21 space straight j with hat on top space plus space 42 space straight k with hat on top right square bracket space equals 1 over 7 left parenthesis 2 straight i with hat on top space plus space 3 straight j with hat on top space plus 6 space straight k with hat on top right parenthesis space equals space straight a with rightwards arrow on top
straight c with rightwards arrow on top cross times space straight a with rightwards arrow on top space equals 1 over 49 open vertical bar table row cell straight i with hat on top end cell cell space straight j with hat on top end cell cell straight k with hat on top end cell row 6 cell space space 2 end cell cell negative 3 end cell row 2 cell space space 3 end cell cell space space 6 end cell end table close vertical bar space equals space 1 over 49 open square brackets left parenthesis 12 plus 9 right parenthesis space straight i with hat on top space minus space left parenthesis 36 plus 6 right parenthesis space straight j with hat on top space plus space left parenthesis 18 minus 4 right parenthesis straight k with hat on top close square brackets space
space space space space space space space space space space space space equals space 1 over 49 left square bracket 21 space straight i with hat on top space minus space 42 space straight j with hat on top space plus space 14 space straight k with hat on top right square bracket space equals space 1 over 7 left parenthesis 3 space straight i with hat on top minus 6 space straight j with hat on top space plus 2 space straight k with hat on top right parenthesis space equals straight b with rightwards arrow on top
    therefore space space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top from a right handed orthogonal system of unit vectors. 


    Question 544
    CBSEENMA12034265

    Find the value of the following:
    straight i with hat on top. space open parentheses straight j with hat on top space cross times space straight k with hat on top close parentheses space plus space straight j with hat on top. space space left parenthesis straight i with hat on top space cross times space straight k with hat on top right parenthesis space plus space space straight k with hat on top. space space left parenthesis straight i with hat on top space cross times space straight j with hat on top right parenthesis

    Solution

    Consider straight i with hat on top. space left parenthesis straight j with hat on top space cross times space straight k with hat on top right parenthesis space plus space straight j with hat on top. space left parenthesis straight i with hat on top space cross times space straight k with hat on top right parenthesis space plus space straight k with hat on top space. space left parenthesis straight i with hat on top space cross times space straight j with hat on top right parenthesis
                    equals space straight i with hat on top. space straight i with hat on top space plus space straight j with hat on top. space left parenthesis negative straight j with hat on top right parenthesis space plus space straight k with hat on top. space straight k with hat on top space equals space straight i with hat on top. space straight i with hat on top space minus space straight j with hat on top space. space straight j with hat on top space plus space straight k with hat on top. space straight k with hat on top
                     equals 1 minus 1 plus 1 space equals 1

    Question 545
    CBSEENMA12034266

    Find the value of the following:
    straight i with hat on top. space left parenthesis straight j with hat on top space cross times space straight k with hat on top right parenthesis space plus space straight j with hat on top space cross times space left parenthesis straight k with hat on top space cross times space straight i with hat on top right parenthesis space plus space straight k with hat on top space cross times space left parenthesis straight i with hat on top space cross times space straight j with hat on top right parenthesis
space

    Solution

    Consider straight i with hat on top. space left parenthesis straight j with hat on top space cross times space straight k with hat on top right parenthesis space plus space straight j with hat on top. space left parenthesis straight k with hat on top space cross times space straight i with hat on top right parenthesis space plus space space straight k with hat on top space. space left parenthesis straight i with hat on top space cross times space straight j with hat on top right parenthesis
                    equals space straight i with hat on top. space straight i with hat on top space plus space straight j with hat on top space. space straight j with hat on top space plus space space straight k with hat on top. space straight k with hat on top
equals space 1 plus 1 plus 1 space equals space 3

    Question 546
    CBSEENMA12034267

    Find the value of the following:
    straight i with hat on top space cross times space left parenthesis straight j with hat on top space cross times space straight k with hat on top right parenthesis space plus space straight j with hat on top space cross times space left parenthesis straight k with hat on top space cross times space straight i with hat on top right parenthesis space plus space straight k with hat on top space cross times space left parenthesis straight i with hat on top space cross times space straight j with hat on top right parenthesis

    Solution

    Consider straight i with hat on top space cross times space left parenthesis straight j with hat on top space cross times space straight k with hat on top right parenthesis space plus space straight j with hat on top space cross times space left parenthesis straight k with hat on top space cross times space straight i with hat on top right parenthesis space plus space straight k with hat on top space cross times space left parenthesis straight i with hat on top space cross times space straight j with hat on top right parenthesis
                          equals space straight i with hat on top space cross times space straight i with hat on top space plus space straight j with hat on top space cross times space straight j with hat on top space plus space straight k with hat on top space cross times space straight k with hat on top
equals space 0 with rightwards arrow on top plus 0 with rightwards arrow on top plus 0 with rightwards arrow on top space equals space 0 with rightwards arrow on top

    Question 547
    CBSEENMA12034268

    Let vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top be such that open vertical bar straight a with rightwards arrow on top close vertical bar space equals 3 space space space and space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space fraction numerator square root of 2 over denominator 3 end fraction comma then straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top is a unit vector, if the angle betweeen straight a with rightwards arrow on top space and space straight b with rightwards arrow on top is 

    • straight pi divided by 6
    • straight pi divided by 4
    • straight pi divided by 3
    • straight pi divided by 2

    Solution

    B.

    straight pi divided by 4

    Here,    open vertical bar straight a with rightwards arrow on top close vertical bar space equals space 3 comma space space space space open vertical bar straight b with rightwards arrow on top close vertical bar space equals fraction numerator square root of 2 over denominator 3 end fraction
    Now,    straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top is a unit vector
    i.e. if open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar space equals space 1
    i.e. if open vertical bar straight a with rightwards arrow on top close vertical bar space open vertical bar straight b with rightwards arrow on top close vertical bar space space sin space straight theta space equals space 1 comma where straight theta is angle between straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.
    i.e. if  left parenthesis 3 right parenthesis space open parentheses fraction numerator square root of 2 over denominator 3 end fraction close parentheses space sin space straight theta space equals space 1
    i.e.   if                     sin space straight theta space equals space fraction numerator 1 over denominator square root of 2 end fraction
    i.e.   if                      straight theta space equals space straight pi over 4
    therefore space space space space space left parenthesis straight B right parenthesis space is space correct space answer.

    Question 549
    CBSEENMA12034270

    The value of straight i with hat on top. space left parenthesis straight j with hat on top space cross times space straight k with hat on top right parenthesis. space plus space straight j with hat on top. space left parenthesis straight i with hat on top space cross times space straight k with hat on top right parenthesis space plus space straight k with hat on top. space left parenthesis straight i with hat on top space cross times space straight j with hat on top right parenthesis is

    • 0

    • -1

    • 1

    • 3

    Solution

    C.

    1

    straight i with hat on top. space left parenthesis straight j with hat on top space cross times space straight k with hat on top right parenthesis space plus space straight j with hat on top. space left parenthesis straight i with hat on top space cross times space straight k with hat on top right parenthesis space plus space straight k with hat on top. space left parenthesis straight i with hat on top space cross times space straight j with hat on top right parenthesis
space space equals space straight i with hat on top space. space straight i with hat on top space plus space straight j with hat on top. space left parenthesis negative straight j with hat on top right parenthesis space plus space straight k with hat on top. space straight k with hat on top space equals space straight i with hat on top. space straight i with hat on top space minus space straight j with hat on top. space straight j with hat on top space plus space straight k with hat on top. space straight k with hat on top
space equals space 1 minus 1 plus 1 space equals space 1
therefore space space left parenthesis straight C right parenthesis space is space correct space answer.
    Question 550
    CBSEENMA12034272

    Area of a rectangle having vertices A, B, C and D with position vectors
    negative straight i with hat on top space plus space 1 half straight j with hat on top space plus space 4 space straight k with hat on top comma space space space straight i with hat on top space plus space 1 half straight j with hat on top space plus space 4 space straight k with hat on top comma space space space space straight i with hat on top space minus space 1 half straight j with hat on top space plus 4 straight k with hat on top space and space minus straight i with hat on top space minus space 1 half straight j with hat on top space plus space 4 straight k with hat on top comma respectively is
    • 1 half
    • 1

    • 2

    • 4

    Solution

    C.

    2

    Position vectors of vertices A, B, C, D of rectangle are
    negative straight i with hat on top space plus space 1 half straight j with hat on top space plus space 4 space straight k with hat on top comma space space space straight i with hat on top space plus space 1 half straight j with hat on top space plus space 4 space straight k with hat on top comma space space space space straight i with hat on top space minus space 1 half straight j with hat on top space plus 4 straight k with hat on top space and space minus straight i with hat on top space minus space 1 half straight j with hat on top space plus space 4 straight k with hat on top comma respectively                 therefore space space space AB with rightwards arrow on top space equals space straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A space equals space open parentheses straight i with hat on top space plus space 1 half straight j with hat on top space plus space 4 space straight k with hat on top close parentheses space minus space open parentheses negative straight i with hat on top space plus space 1 half straight j with hat on top space plus space 4 space straight k with hat on top close parentheses space equals space 2 space straight i with hat on top
      space and space AD with rightwards arrow on top space equals space straight P. straight V. space of space straight D space minus space straight P. straight V. space of space straight A
space space space space space space equals space open parentheses negative straight i with hat on top space minus space 1 half straight j with hat on top space plus space 4 space straight k with hat on top close parentheses space minus space open parentheses negative straight i with hat on top space plus space 1 half straight j with hat on top space plus space 4 space straight k with hat on top close parentheses space equals space minus straight j with hat on top
AB with rightwards arrow on top space cross times space AD with rightwards arrow on top space equals space 2 space straight i with hat on top space cross times space left parenthesis negative straight j with hat on top right parenthesis space equals space minus 2 space left parenthesis straight i with hat on top space cross times space straight j with hat on top right parenthesis space equals space minus 2 space straight k with hat on top
therefore space space area space of space rectangle space space equals space open vertical bar AB with rightwards arrow on top space cross times space AD with rightwards arrow on top close vertical bar space equals space left parenthesis negative 2 space straight k with hat on top right parenthesis space equals space 2
therefore space space left parenthesis straight C right parenthesis space is space correct space answer.
    Question 551
    CBSEENMA12034273

    If A, B and C are the vertices of a triangle ABC, prove Sine Formula that
    fraction numerator straight a over denominator sin space straight A end fraction space equals space fraction numerator straight b over denominator sin space straight B end fraction space equals space fraction numerator straight c over denominator sin space straight C end fraction.

    Solution

     Let space BC with rightwards arrow on top space equals space straight a with rightwards arrow on top comma space space CA with rightwards arrow on top space equals space straight b with rightwards arrow on top comma space space AB with rightwards arrow on top space equals space straight c with rightwards arrow on top space so space that space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space equals space minus straight c with rightwards arrow on top
therefore space space space space straight a with rightwards arrow on top space cross times space straight a with rightwards arrow on top space plus space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space minus straight a with rightwards arrow on top cross times space straight c with rightwards arrow on top
therefore space space space space 0 with rightwards arrow on top space plus space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top space cross times space straight a with rightwards arrow on top
therefore space space space space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space straight c with rightwards arrow on top space cross times space straight a with rightwards arrow on top
therefore space space space space space open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight c with rightwards arrow on top space cross times space straight a with rightwards arrow on top close vertical bar
therefore space space straight a space straight b space sin space left parenthesis 180 degree minus straight C right parenthesis space equals space straight c space straight a space sin space left parenthesis 180 degree space minus space straight B right parenthesis
therefore space space space straight a space straight b space sin space straight C space equals space straight c space straight a space sin space straight B

    Dividing both sides by a, b,  c we get,
                   fraction numerator sin space straight C over denominator straight c end fraction space equals space fraction numerator sin space straight B over denominator straight b end fraction comma space space space space space space space therefore space space space fraction numerator straight b over denominator sin space straight B end fraction space equals space fraction numerator straight c over denominator sin space straight C end fraction
    Similarly,          fraction numerator straight c over denominator sin space straight C end fraction space equals space fraction numerator straight a over denominator sin space straight A end fraction                                                 ...(1)
    From (1) and (2), we have
                 fraction numerator straight a over denominator sin space straight A end fraction space equals space fraction numerator straight b over denominator sin space straight B end fraction space equals space fraction numerator straight c over denominator sin space straight C end fraction.

    Question 552
    CBSEENMA12034275

    Using vectors, prove that sin (A + B) = sin A + cos B + cos A sin B. 

    Solution
    Let OP and OQ be unit vectors making angles A and B with X-axis such that
    angle space POQ space equals space straight A plus straight B
    therefore space space space space space OP with rightwards arrow on top space equals space straight i with hat on top space cos space straight A space plus space straight j with hat on top space sin space straight A
space space space space space space space space space OQ with rightwards arrow on top space equals space straight i with hat on top space cos space straight B space minus space straight j with hat on top space sin space straight A
Now comma space OP with rightwards arrow on top space cross times space OQ with rightwards arrow on top space equals space left parenthesis 1 right parenthesis thin space left parenthesis 1 right parenthesis space sin space left parenthesis straight A plus straight B right parenthesis space left parenthesis negative straight k with hat on top space right parenthesis space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space
therefore space space space space OP with rightwards arrow on top space cross times space OQ with rightwards arrow on top space equals space sin space left parenthesis straight A plus straight B right parenthesis space straight k with hat on top space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
Also comma space space space OP with rightwards arrow on top space cross times space OQ with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row cosA sinA 0 row cosB cell negative sinB end cell 0 end table close vertical bar space equals space left parenthesis negative cos space straight A space sin space straight B space minus space sin space straight A space cos space straight B right parenthesis space straight k with hat on top
therefore space space space space OP with rightwards arrow on top space cross times space OQ with rightwards arrow on top space equals space minus left parenthesis sin space straight A space cos space straight B space plus space cos space straight A space sin space straight B right parenthesis space straight k with hat on top space space space space space space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis

    From (1) and (2), we get,
                            sin space left parenthesis straight A plus straight B right parenthesis space equals space sin space straight A space cos space straight B space plus space cos space straight A space sin space straight B.
    Question 553
    CBSEENMA12034277

    Prove by vector method that sin (A – B) = sin A cos B – cos A sin B

    Solution
    Let OX and OY be two axes and let straight I with hat on top space and space straight j with hat on top be unit vectors along OX and OY respectively.

              Let  OP with rightwards arrow on top space and space OQ with rightwards arrow on top be two vectors such that 
         angle XOP space equals space straight A space and space angle XOQ space space equals space straight B so that
                    angle POQ space equals space space straight A space minus space straight B.
            Draw PL space perpendicular space OX comma space space QM space perpendicular space OX.
             Let space straight k with hat on top be the unit vector along z-axis.
             Now,        OP with rightwards arrow on top space equals space OL with rightwards arrow on top space plus space LP with rightwards arrow on top
                                    equals space left parenthesis OP space cos space straight A right parenthesis straight i with hat on top space plus space left parenthesis OP space sin space straight A right parenthesis straight j with hat on top                              
    and         OQ with rightwards arrow on top space equals space OM with rightwards arrow on top space plus space MQ with rightwards arrow on top
                           equals space left parenthesis OQ space cos space straight B right parenthesis space straight i with hat on top space plus space left parenthesis OQ space sin space straight B right parenthesis space straight j with hat on top
    therefore space space space OP with rightwards arrow on top space cross times space OQ with rightwards arrow on top space equals space open square brackets left parenthesis OP space cos space straight A right parenthesis space straight i with hat on top space plus space left parenthesis OP space sin space straight A right parenthesis space straight j with hat on top close square brackets space cross times space open square brackets left parenthesis OQ space cos space straight B right parenthesis straight i with hat on top plus space left parenthesis OQ space sin space straight B right parenthesis space straight j with hat on top close square brackets
                              equals space OP. space OQ space open square brackets left parenthesis cos space straight A right parenthesis space straight i with hat on top space plus space sin space straight A right parenthesis space straight j with hat on top close square brackets space cross times space open square brackets left parenthesis cos space straight B right parenthesis straight i with hat on top space plus space left parenthesis sin space straight B right parenthesis straight j with hat on top close square brackets
equals space OP. space OQ space open square brackets left parenthesis cos space straight A space sin space straight B right parenthesis thin space left parenthesis straight i with hat on top space cross times space straight j with hat on top right parenthesis space plus space left parenthesis sin space straight A space cos space straight B right parenthesis thin space left parenthesis straight j with hat on top space cross times straight i with hat on top space right parenthesis close square brackets
space equals space OP. space OQ space left square bracket cos space straight A space sin space straight B space straight k with hat on top space minus space sin space straight A space cos space straight B space straight k with hat on top right square bracket
space equals space OP. space OQ space left square bracket cos space straight A space sin space straight B space minus space sin space straight A space cos space straight B right square bracket space straight k with hat on top space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
    Also,   OP with rightwards arrow on top space cross times space OQ with rightwards arrow on top space equals space open vertical bar OP with rightwards arrow on top close vertical bar space open vertical bar OQ with rightwards arrow on top close vertical bar space sin space left parenthesis straight A minus straight B right parenthesis space left parenthesis negative straight k with hat on top right parenthesis
                                             equals space space minus OP. space OQ space sin space left parenthesis straight A minus straight B right parenthesis space straight k with hat on top                                         ...(2)
    From (1) and (2), we get
                             cos space straight A space sin space straight B space minus space sin space straight A space cos space straight B space equals space minus sin space left parenthesis straight A minus straight B right parenthesis
    therefore space space space space space space space space space space space space space space space space space space   sin left parenthesis straight A minus straight B right parenthesis space equals space sin space straight A space cos space straight B space minus space cos space straight A space sin space straight B.
    Question 554
    CBSEENMA12034278

    Prove that the parallelograms on the same base and between the same parallels are equal in area.

    Solution
    Let OACB and OAED be two parallelograms on the same base OA and between the same parallels are equal in area.
    Let  OA with rightwards arrow on top space equals space straight a with rightwards arrow on top space space and space OB with rightwards arrow on top space equals space straight b with rightwards arrow on top
    Since BD is parallel to OA,
       therefore space space space space space space BD with rightwards arrow on top space equals space straight x straight a with rightwards arrow on top comma space where space straight x space is space some space scalar.
therefore space space space space space space space OD with rightwards arrow on top space equals space OB with rightwards arrow on top space plus space BD with rightwards arrow on top space equals space straight b with rightwards arrow on top space plus space straight x space straight a with rightwards arrow on top

    Now vector area of parallelogram OAED = OA with rightwards arrow on top space cross times space OD with rightwards arrow on top
                            equals space straight a with rightwards arrow on top space cross times space left parenthesis straight b with rightwards arrow on top space plus space straight x space straight a with rightwards arrow on top right parenthesis space equals space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space plus space straight x space straight a with rightwards arrow on top space cross times space straight a with rightwards arrow on top
space equals space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space plus space 0 with rightwards arrow on top space equals space straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space space straight a with rightwards arrow on top space cross times space straight a with rightwards arrow on top space equals space 0 with rightwards arrow on top close square brackets
space equals space OA with rightwards arrow on top space cross times space OB with rightwards arrow on top space equals space vector space area space of space parallelogram space OACB.
    Question 555
    CBSEENMA12034280

    If D, E, F are the mid points of the sides of triangle ABC, prove that
    area left parenthesis increment DEF right parenthesis space equals space 1 fourth area space left parenthesis increment thin space ABC right parenthesis.

    Solution
    Take A as origin. Let position vectors of B and C be straight b with rightwards arrow on top space and space straight c with rightwards arrow on top respectively.
    therefore  position vectors of D, E, F are 1 half left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis comma space space space space 1 half straight c with rightwards arrow on top space and space space 1 half straight b with rightwards arrow on top space respectively.
    therefore space space DE with rightwards arrow on top space equals space left parenthesis straight P. straight V. space of space straight E right parenthesis space minus space left parenthesis straight P. straight V. space of space straight D right parenthesis
space space space space space space space space space space space space space equals space 1 half straight c with rightwards arrow on top space minus space 1 half left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space equals space minus 1 half straight b with rightwards arrow on top
and space DF with rightwards arrow on top space equals space left parenthesis straight P. straight V. space of space straight F right parenthesis space space minus space left parenthesis straight P. straight V. space of space straight D right parenthesis
space space space space space space space space space space space space space space equals space 1 half straight b with rightwards arrow on top space minus space 1 half left parenthesis straight b with rightwards arrow on top plus straight c with rightwards arrow on top right parenthesis space equals space minus 1 half straight c with rightwards arrow on top

    therefore space space vector space area space of space increment DEF space equals space 1 half DE with rightwards arrow on top space cross times space DF with rightwards arrow on top
space space equals space 1 half open parentheses negative 1 half straight b with rightwards arrow on top close parentheses space cross times space open parentheses negative 1 half straight c with rightwards arrow on top close parentheses space equals 1 fourth space open parentheses 1 half space left parenthesis straight b with rightwards arrow on top space cross times space stack straight c right parenthesis with rightwards arrow on top close parentheses
space equals space 1 fourth left parenthesis vector space area space of space increment ABC right parenthesis.
    Hence the result. 

    Question 556
    CBSEENMA12035629

    find space straight lambda space and space straight mu space if

open parentheses straight i with hat on top plus space 3 space straight j with hat on top space plus space 9 space straight k with hat on top close parentheses space space straight x space space left parenthesis 3 space straight i with hat on top plus straight lambda space straight j with hat on top plus space straight mu space straight k with hat on top right parenthesis space equals space 0

    Solution
    open parentheses straight i with hat on top plus space 3 space straight j with hat on top plus space 9 space straight k with hat on top close parentheses space space straight x space left parenthesis 3 space straight i with hat on top plus straight lambda space straight j with hat on top plus space straight mu space straight k with hat on top right parenthesis space equals 0

open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 1 3 9 row 3 cell negative straight lambda end cell straight mu end table close vertical bar space equals 0

straight i with hat on top left parenthesis 3 straight mu space plus space 9 straight lambda right parenthesis minus straight j with hat on top left parenthesis straight mu minus 27 right parenthesis space plus space straight k with hat on top left parenthesis negative straight lambda minus 9 right parenthesis space equals 0

3 straight mu space plus space 9 straight lambda space equals 0 space space..... space left parenthesis straight i right parenthesis

27 minus straight mu space equals 0 space space space....... left parenthesis ii right parenthesis

minus straight lambda minus 9 space equals 0 space...... space left parenthesis iii right parenthesis

By space equation space left parenthesis ii right parenthesis space and space left parenthesis iii right parenthesis space

straight mu space equals space 27 space and space straight lambda space equals space minus 9

straight lambda comma space straight mu space value space satisfy space the space equation space left parenthesis straight i right parenthesis

so space space straight mu space equals space 27 comma space straight lambda space equals negative 9
    Question 557
    CBSEENMA12035630

    If space straight a with rightwards arrow on top equals 4 space straight i with hat on top space minus straight j with hat on top plus space straight k with hat on top space and space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space minus 2 straight j with hat on top plus space straight k with hat on top comma then space find space straight a space vector space parallel space to space the space vector space straight a with rightwards arrow on top plus straight b with rightwards arrow on top.

    Solution
    Given comma
straight a with rightwards arrow space on top equals space 4 space straight i with hat on top space minus straight j with hat on top plus space straight k with hat on top space and space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space minus 2 straight j with hat on top plus space straight k with hat on top

therefore space straight a with rightwards arrow on top plus straight b with rightwards arrow on top space equals space open parentheses 4 space straight i with hat on top space minus straight j with hat on top plus space straight k with hat on top close parentheses space plus space open parentheses 2 space straight i with hat on top space minus 2 straight j with hat on top plus space straight k with hat on top close parentheses

equals 6 space straight i with hat on top space minus space 3 straight j with hat on top space plus space 2 straight k with hat on top
unit space vector space parallel space to space left parenthesis straight a with rightwards arrow on top plus straight b with rightwards arrow on top right parenthesis space space equals space fraction numerator straight a with rightwards arrow on top plus straight b with rightwards arrow on top over denominator vertical line straight a with rightwards arrow on top plus straight b with rightwards arrow on top vertical line end fraction
equals space fraction numerator 6 space straight i with hat on top minus 3 straight j with hat on top plus 2 straight k with hat on top over denominator square root of 36 plus 9 plus 4 end root end fraction

equals space fraction numerator 6 space straight i with hat on top minus 3 straight j with hat on top plus 2 straight k with hat on top over denominator square root of 49 end fraction

equals fraction numerator 6 space straight i with hat on top over denominator 7 end fraction minus fraction numerator 3 straight j with hat on top over denominator 7 end fraction plus fraction numerator 2 straight k with hat on top over denominator 7 end fraction
    Question 561
    CBSEENMA12035657

    If straight a with rightwards arrow on top space equals space 2 straight i with hat on top plus straight j with hat on top plus 3 straight k with hat on top space space space and space straight b with rightwards arrow on top space equals space 3 straight i with hat on top space plus space 5 straight j with hat on top space minus space 2 straight k with hat on top comma space then space find space open vertical bar straight a with rightwards arrow on top cross times space straight b with rightwards arrow on top close vertical bar.

    Solution
    Given space that space straight a with rightwards arrow on top space equals space 2 straight i with hat on top space plus space straight j with hat on top space plus space 3 straight k with hat on top space space and space straight b with rightwards arrow on top space equals space 3 straight i with hat on top space plus space 5 straight j with hat on top space minus space 2 straight k with hat on top
We space need space to space find space open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar
straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 2 1 3 row 3 5 cell negative 2 end cell end table close vertical bar
space space space equals space straight i with hat on top left parenthesis negative 2 minus 15 right parenthesis space minus space straight j with hat on top left parenthesis negative 4 minus 9 right parenthesis space plus space straight k with hat on top left parenthesis 10 minus 3 right parenthesis
space space space space equals negative 17 straight i with hat on top space plus space 13 straight j with hat on top space plus space 7 straight k with hat on top
Hence comma space open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar space equals space square root of 17 squared plus 13 squared plus 7 squared end root
space space space space space space space space equals open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar space equals space square root of 507
    Question 562
    CBSEENMA12035658
    Question 563
    CBSEENMA12035661

    Find the differential equation of the family of lines passing through the origin. 

    Solution

    Consider the equation, y = mx, where m is the parameter.
    Thus, the above equation represents the family of lines which pass through the origin.
    y = mx    ....(1)
     rightwards double arrow space space straight y over straight x space equals space straight m space... left parenthesis 2 right parenthesis 
    Differentiating the above equation (1) which respect to x,
       straight y space equals space mx
dy over dx space equals space straight m space cross times space 1
space space rightwards double arrow space space dy over dx equals straight m
space space space rightwards double arrow space dy over dx space equals space straight y over straight x space left square bracket because space from space equation space left parenthesis 2 right parenthesis right square bracket
space space space space rightwards double arrow dy over dx minus space straight y over straight x space equals space 0

space
    Thus we have eliminated the constant, m.
    The required differential equation is
    dy over dx minus straight y over straight x space equals 0

    Question 564
    CBSEENMA12035675

    If space straight y space equals space straight e to the power of ax. cosbx comma space then space prove space that
space space space fraction numerator straight d squared straight y over denominator dx squared end fraction minus 2 straight a dy over dx plus left parenthesis straight a squared plus straight b squared right parenthesis straight y space equals space 0

    Solution
    straight y equals straight e to the power of ax. cos space bx
dy over dx equals ae to the power of ax. cosbx minus be to the power of ax. sinbx space space... left parenthesis straight i right parenthesis
dy over dx equals ay minus be to the power of ax. space sinbx
fraction numerator straight d squared straight y over denominator dx squared end fraction equals straight a dy over dx minus straight b left parenthesis ae to the power of ax. sinbx plus be to the power of ax. cosbx right parenthesis
fraction numerator straight d squared straight y over denominator dx squared end fraction equals straight a dy over dx minus abe to the power of ax. sinbx minus straight b squared straight e to the power of ax. cos space bx
fraction numerator straight d squared straight y over denominator dx squared end fraction equals straight a dy over dx minus straight a open parentheses ay minus dy over dx close parentheses minus straight b squared straight y space left square bracket Substituting space be to the power of ax space sinbx space from space left parenthesis straight i right parenthesis right square bracket
    fraction numerator straight d squared straight y over denominator dx squared end fraction space equals straight a dy over dx minus straight a squared straight y plus straight a dy over dx minus straight b squared straight y
therefore space space space fraction numerator straight d squared straight y over denominator dx squared end fraction minus 2 straight a dy over dx plus left parenthesis straight a squared plus straight b squared right parenthesis straight y space equals space 0
    Hence Proved


    Question 565
    CBSEENMA12035676

    If space straight x to the power of straight x plus straight x to the power of straight y plus straight y to the power of straight x space equals space straight a to the power of straight b comma space space then space find space dy over dx.

    Solution
    straight x to the power of straight x plus straight x to the power of straight y plus straight y to the power of straight x space equals straight a to the power of straight b space space space... left parenthesis straight i right parenthesis
Let space straight u space equals space straight x to the power of straight x
log space straight u space equals space straight x space log space straight x
1 over straight u. du over dx equals straight x.1 over straight x plus log space straight x
therefore space space du over dx equals straight x to the power of straight x left parenthesis 1 plus log space straight x right parenthesis
Let space straight v equals space straight x to the power of straight y
log space straight v space equals space straight y space log space straight x
1 over straight v. dv over dx space equals space open parentheses straight y over straight x plus log space straight x dy over dx close parentheses
therefore space dv over dx equals straight x to the power of straight y open parentheses straight y over straight x plus logx dy over dx close parentheses
Let space straight w space equals straight y to the power of straight x
Log space straight w space equals space straight x space log space straight y
1 over straight w. dw over dx equals space open parentheses straight x over straight y. dy over dx plus log space straight y close parentheses
therefore space dw over dx equals straight y to the power of straight x open parentheses log space straight y space plus space straight x over straight y. dy over dx close parentheses
    left parenthesis straight i right parenthesis space can space be space writeen space as
straight u plus straight v plus straight w space equals space straight a to the power of straight b
du over dx plus dv over dx plus dw over dx equals 0
rightwards double arrow space space straight x to the power of straight x left parenthesis 1 plus logx right parenthesis plus straight x to the power of straight y open parentheses straight y over straight x plus logx dy over dx close parentheses plus straight y to the power of straight x open parentheses logy plus straight x over straight y dy over dx close parentheses space equals space 0
rightwards double arrow space space straight x to the power of straight x plus straight x to the power of straight x logx plus straight x to the power of straight y. straight y over straight x plus straight x to the power of straight y. logx. dy over dx plus straight y to the power of straight x. logy plus straight y to the power of straight x. straight x over straight y. dy over dx equals 0
rightwards double arrow space space dy over dx open parentheses straight x to the power of straight y. logx space plus space straight y to the power of straight x. straight x over straight y close parentheses space equals space straight x to the power of straight x plus straight x to the power of straight x logx plus straight x to the power of straight y. straight y over straight x plus straight y to the power of straight x. log space straight y
rightwards double arrow dy over dx open parentheses straight x to the power of straight y. logx space plus space xy to the power of straight x minus 1 end exponent close parentheses space equals space open parentheses straight x to the power of straight x plus straight x to the power of straight x logx plus yx to the power of straight y minus 1 end exponent plus straight y to the power of straight x. log space straight y close parentheses
therefore space space dy over dx equals fraction numerator left parenthesis straight x to the power of straight x plus straight x to the power of straight x logx space plus yx to the power of straight y minus 1 end exponent plus straight y to the power of straight x. log space straight y right parenthesis over denominator left parenthesis straight x to the power of straight y. logx plus xy to the power of straight x minus 1 end exponent right parenthesis end fraction
    Question 566
    CBSEENMA12035677

    If straight x equals straight a space sin space 2 straight t left parenthesis 1 plus cos space 2 straight t right parenthesis space and space straight y space equals straight b space cos space 2 straight t left parenthesis 1 minus cos space 2 straight t right parenthesis comma space then space find dy over dx space at space straight t space equals straight pi over 4.

    Solution
    straight x equals straight a space sin space 2 straight t left parenthesis 1 plus cos space 2 straight t right parenthesis comma
straight y equals space straight b space cos space 2 straight t left parenthesis 1 minus cos space 2 straight t right parenthesis
dx over dt space equals 2 straight a space cos space 2 straight t left parenthesis 1 plus cos space 2 straight t right parenthesis space plus space straight a space sin space 2 straight t left parenthesis negative 2 space sin space 2 straight t right parenthesis
space space space space equals space 2 straight a space cos 2 straight t space plus space 2 acos squared 2 straight t minus 2 straight a space sin squared 2 straight t
space space space space equals 2 acos 2 straight t space plus space 2 acos 4 straight t
space space space space dy over dt equals negative 2 bsin 2 straight t left parenthesis 1 minus cost space 2 straight t right parenthesis plus bcos 2 straight t left parenthesis 2 sin 2 straight t right parenthesis
space space space space space space space equals space minus 2 bsin 2 straight t space plus 2 bsin space 2 tcos 2 straight t space plus 2 bcos 2 straight t space sin 2 straight t
space space space space space space space equals negative 2 bsin 2 straight t plus 4 bsin 2 tcos 2 straight t
space space space space space space space equals negative 2 bsin 2 straight t plus 2 bsin 4 straight t
         fraction numerator begin display style dy over dt end style over denominator begin display style dx over dt end style end fraction equals fraction numerator negative 2 bsin 2 straight t plus 2 bsin 4 straight t over denominator 2 acos 2 straight t plus 2 acos 4 straight t end fraction
space space space rightwards double arrow space space space dy over dx equals fraction numerator negative 2 bsin 2 straight t plus 2 bsin 4 straight t over denominator 2 acos 2 straight t plus 2 acos 4 straight t end fraction
space space space space space rightwards double arrow space open vertical bar dy over dx close vertical bar subscript straight t equals straight pi over 4 end subscript space equals space fraction numerator negative 2 bsin begin display style fraction numerator 2 straight pi over denominator 4 end fraction end style plus 2 bsin begin display style fraction numerator 4 straight pi over denominator 4 end fraction end style over denominator 2 acos begin display style fraction numerator 2 straight pi over denominator 4 end fraction end style plus 2 acos begin display style fraction numerator 4 straight pi over denominator 4 end fraction end style end fraction
space space space space space rightwards double arrow open vertical bar dy over dx close vertical bar subscript straight t equals straight pi over 4 end subscript space equals fraction numerator negative 2 bsin begin display style straight pi over 2 end style plus 2 bsinπ over denominator 2 acos begin display style straight pi over 2 end style plus 2 acosπ end fraction
space space space space space rightwards double arrow open vertical bar dy over dx close vertical bar subscript straight t equals straight pi over 4 end subscript space equals fraction numerator negative 2 straight b over denominator negative 2 straight a end fraction equals straight b over straight a
space space space space space space space space therefore space space space open vertical bar dy over dx close vertical bar subscript straight t equals straight pi over 4 end subscript space equals straight b over straight a
space space space space space space space space space
    Question 567
    CBSEENMA12035682

    Sketch the region bounded by the curves straight y equals square root of 5 minus straight x squared end root space and space straight y space equals open vertical bar straight x minus 1 close vertical bar and find its area using integration. 

    Solution

    Consider the given equation. 
    straight y equals square root of 5 minus straight x squared end root
    This equation represents a semicircle with centre at the origin and radius  = square root of 5 space units
    Given that the region is bounded by the above semicircle and the line straight y equals open vertical bar straight x minus 1 close vertical bar
    Let us find the point of intersection of the given curve meets the line straight y equals open vertical bar straight x minus 1 close vertical bar
    rightwards double arrow square root of 5 minus straight x squared end root space equals space open vertical bar straight x minus 1 close vertical bar
    Squaring both the sides, we have,
    5 minus straight x squared space equals open vertical bar straight x minus 1 close vertical bar squared
rightwards double arrow 5 minus straight x squared space equals space straight x squared plus 1 minus 2 straight x
rightwards double arrow 2 straight x squared minus 2 straight x minus 5 plus 1 space equals space 0
rightwards double arrow 2 straight x squared minus 2 straight x minus 4 space equals space 0
rightwards double arrow straight x squared minus straight x minus 2 space equals 0
rightwards double arrow space straight x squared minus 2 straight x plus straight x minus 2 space equals 0
rightwards double arrow straight x left parenthesis straight x minus 2 right parenthesis plus 1 left parenthesis straight x minus 2 right parenthesis equals 0
rightwards double arrow left parenthesis straight x plus 1 right parenthesis thin space left parenthesis straight x minus 2 right parenthesis space equals space 0
rightwards double arrow straight x space equals negative 1 comma space straight x space equals space 2
When space straight x space equals space minus 1 comma space space straight y space equals space 2
When space straight x space equals space 2 comma space space straight y space equals space 1
    Consider the following figure
    Thus the intersection points are 1,2 and 2,1 ( ) ( ) Consider the following sketch of the bounded region.

    Required Area, straight A space equals space integral subscript negative 1 end subscript superscript 2 left parenthesis straight y subscript 2 minus straight y subscript 1 right parenthesis dx space
    equals integral subscript negative 1 end subscript superscript 1 space open square brackets square root of 5 minus straight x squared end root plus left parenthesis straight x minus 1 right parenthesis close square brackets dx space plus space integral subscript 1 superscript 2 space open square brackets square root of 5 minus straight x squared end root minus left parenthesis straight x minus 1 right parenthesis close square brackets dx
equals integral subscript negative 1 end subscript superscript 1 space square root of 5 minus straight x squared end root dx plus integral subscript negative 1 end subscript superscript 1 xdx space minus integral subscript negative 1 end subscript superscript 1 dx space plus space integral subscript 1 superscript 2 square root of 5 minus straight x squared end root dx minus integral subscript 1 superscript 2 xdx plus integral subscript 1 superscript 2 dx
equals open square brackets straight x over 2 square root of 5 minus straight x squared end root plus 5 over 2 sin to the power of negative 1 end exponent open parentheses fraction numerator straight x over denominator square root of 5 end fraction close parentheses close square brackets subscript negative 1 end subscript superscript 1 space plus space open parentheses straight x squared over 2 close parentheses subscript negative 1 end subscript superscript 1 space minus left parenthesis straight x right parenthesis subscript negative 1 end subscript superscript 1 plus open square brackets straight x over 2 square root of 5 minus straight x squared end root plus 5 over 2 sin to the power of negative 1 end exponent open parentheses fraction numerator straight x over denominator square root of 5 end fraction close parentheses close square brackets subscript 1 superscript 2
minus open parentheses straight x squared over 2 close parentheses subscript 1 superscript 2 space plus left parenthesis straight x right parenthesis subscript 1 superscript 2
equals 5 over 2 sin to the power of negative 1 end exponent open parentheses fraction numerator 1 over denominator square root of 5 end fraction close parentheses plus 5 over 2 sin to the power of negative 1 end exponent open parentheses fraction numerator 2 over denominator square root of 5 end fraction close parentheses minus 1 half
    Required space Area space equals open square brackets 5 over 2 sin to the power of negative 1 end exponent open parentheses fraction numerator 1 over denominator square root of 5 end fraction close parentheses plus 5 over 2 sin to the power of negative 1 end exponent open parentheses fraction numerator 2 over denominator square root of 5 end fraction close parentheses minus 1 half close square brackets sq. space units

    Question 569
    CBSEENMA12035684

    Find the particulars solution of the differential equation left parenthesis 1 plus straight x squared right parenthesis dy over dx equals open parentheses straight e to the power of straight m space tan to the power of negative 1 straight x end exponent end exponent minus straight y close parentheses comma space given space that space straight y space equals space 1 space when space straight x space equals space 0.

    Solution
    left parenthesis 1 plus straight x squared right parenthesis dy over dx space equals space straight e to the power of straight m space tan to the power of negative 1 straight x end exponent end exponent minus straight y
rightwards double arrow dy over dx equals fraction numerator straight e to the power of mtan to the power of negative 1 end exponent straight x end exponent over denominator left parenthesis 1 plus straight x squared right parenthesis end fraction minus fraction numerator straight y over denominator left parenthesis 1 plus straight x squared right parenthesis end fraction
rightwards double arrow dy over dx plus fraction numerator straight y over denominator left parenthesis 1 plus straight x squared right parenthesis end fraction equals fraction numerator straight e to the power of mtan to the power of negative 1 end exponent straight x end exponent over denominator left parenthesis 1 plus straight x squared right parenthesis end fraction
straight P space equals fraction numerator 1 over denominator left parenthesis 1 plus straight x squared right parenthesis end fraction comma space straight Q equals fraction numerator straight e to the power of mtan to the power of negative 1 end exponent straight x end exponent over denominator left parenthesis 1 plus straight x squared right parenthesis end fraction
straight I. straight F. space equals space straight e to the power of integral Pdx end exponent
space space space space space equals straight e to the power of integral fraction numerator dx over denominator left parenthesis 1 plus straight x squared right parenthesis end fraction end exponent
space space space space space space equals straight e to the power of tan to the power of negative 1 end exponent straight x end exponent
    Thus the solution is
    ye to the power of integral Pdx end exponent space equals integral Qe to the power of integral Pdx end exponent dx
rightwards double arrow space space straight y cross times straight e to the power of tan to the power of negative 1 end exponent straight x end exponent space space equals integral fraction numerator straight e to the power of straight m space tan to the power of negative 1 end exponent straight x end exponent over denominator left parenthesis 1 plus straight x squared right parenthesis end fraction straight e to the power of tan to the power of negative 1 end exponent straight x end exponent. dx
rightwards double arrow space straight y cross times straight e to the power of tan to the power of negative 1 end exponent straight x end exponent space equals space integral fraction numerator straight e to the power of left parenthesis straight m plus 1 right parenthesis tan to the power of negative 1 end exponent straight x end exponent over denominator left parenthesis 1 plus straight x squared right parenthesis end fraction dx.... left parenthesis straight i right parenthesis
integral fraction numerator straight e to the power of left parenthesis straight m plus 1 right parenthesis tan to the power of negative 1 end exponent straight x end exponent over denominator left parenthesis 1 plus straight x squared right parenthesis end fraction dx space.... left parenthesis ii right parenthesis
Let space left parenthesis straight m plus 1 right parenthesis tan to the power of negative 1 end exponent straight x space equals straight z
fraction numerator left parenthesis straight m plus 1 right parenthesis over denominator left parenthesis 1 plus straight x squared right parenthesis end fraction dx space equals space dz
fraction numerator dx over denominator left parenthesis 1 plus straight x squared right parenthesis end fraction dx space equals space dz
fraction numerator dx over denominator left parenthesis 1 plus straight x squared right parenthesis end fraction equals space fraction numerator dz over denominator left parenthesis straight m plus 1 right parenthesis end fraction
    Substituting in (ii),
      fraction numerator 1 over denominator left parenthesis straight m plus 1 right parenthesis end fraction integral straight e to the power of straight z dz
equals fraction numerator straight e to the power of straight z over denominator left parenthesis straight m plus 1 right parenthesis end fraction
equals fraction numerator straight e to the power of left parenthesis straight m plus 1 right parenthesis tan to the power of negative 1 end exponent straight x end exponent over denominator left parenthesis straight m plus 1 right parenthesis end fraction
    Substituting in (i),
    rightwards double arrow straight y cross times straight e to the power of tan to the power of negative 1 end exponent straight x end exponent space equals space fraction numerator straight e to the power of left parenthesis straight m plus 1 right parenthesis tan to the power of negative 1 end exponent straight x end exponent over denominator left parenthesis straight m plus 1 right parenthesis end fraction plus straight C space.... left parenthesis iii right parenthesis
Putting space straight y space equals space 1 space and space straight x space equals space 1 comma space in space the space above space equation comma
space space rightwards double arrow space space straight y space cross times space straight e to the power of tan to the power of negative 1 end exponent 1 end exponent space equals fraction numerator straight e to the power of left parenthesis straight m plus 1 right parenthesis tan to the power of negative 1 end exponent 1 end exponent over denominator left parenthesis straight m plus 1 right parenthesis end fraction plus straight C
space rightwards double arrow 1 cross times straight e to the power of straight pi over 4 end exponent space equals space fraction numerator straight e to the power of left parenthesis straight m plus 1 right parenthesis end exponent begin display style straight pi over 4 end style over denominator left parenthesis straight m plus 1 right parenthesis end fraction plus straight C
therefore straight C space equals space fraction numerator straight e to the power of left parenthesis straight m plus 1 right parenthesis begin display style straight pi over 4 end style end exponent over denominator left parenthesis straight m plus 1 right parenthesis end fraction minus straight e to the power of straight pi over 4 end exponent
    Particular solution of the D.E. is straight y cross times straight e to the power of tan to the power of negative 1 end exponent straight x end exponent space equals space fraction numerator straight e to the power of left parenthesis straight m plus 1 right parenthesis tan to the power of negative 1 end exponent straight x end exponent over denominator left parenthesis straight m plus 1 right parenthesis end fraction plus fraction numerator straight e to the power of left parenthesis straight m plus 1 right parenthesis begin display style straight pi over 4 end style end exponent over denominator left parenthesis straight m plus 1 right parenthesis end fraction minus straight e to the power of straight pi over 4 end exponent
     
    Question 570
    CBSEENMA12035694

    Find the value of 'p' for which the vectors 3 straight i with hat on top plus 2 straight j with hat on top plus 9 straight k with hat on top space and space straight i with hat on top minus 2 straight p straight j with hat on top plus 3 straight k with hat on top are parallel.

    Solution

    Since the vectors are parallel, we have
    straight a with rightwards harpoon with barb upwards on top equals straight lambda straight b with rightwards harpoon with barb upwards on top
    rightwards double arrow 3 straight i with hat on top plus 2 straight j with hat on top plus 9 straight k space equals space straight lambda open parentheses straight i minus 2 straight p straight j with hat on top space plus 3 straight k close parentheses
rightwards double arrow 3 straight i with hat on top plus 2 straight j with hat on top plus 9 straight k space equals space straight lambda straight i with hat on top minus 2 λp straight j with hat on top plus 3 λk
Comparing space the space respective space coefficients comma space we space have
rightwards double arrow space space straight lambda space equals space 3 semicolon
minus 2 λp space equals space 2
rightwards double arrow negative 2 cross times 3 cross times straight p space equals space 2
rightwards double arrow straight p equals fraction numerator negative 1 over denominator 3 end fraction

    Question 571
    CBSEENMA12035696

    If the cartesian equations of a line are fraction numerator 3 minus straight x over denominator 5 end fraction equals fraction numerator straight y plus 4 over denominator 7 end fraction equals fraction numerator 2 straight z minus 6 over denominator 4 end fraction comma write the vector equation for the line. 

    Solution

    Given that the cartesian equation of the line as 
    fraction numerator 3 minus straight x over denominator 5 end fraction equals fraction numerator straight y plus 4 over denominator 7 end fraction equals fraction numerator 2 straight z minus 6 over denominator 4 end fraction
That space is comma
fraction numerator negative left parenthesis straight x minus 3 right parenthesis over denominator 5 end fraction equals fraction numerator straight y minus left parenthesis negative 4 right parenthesis over denominator 7 end fraction equals fraction numerator 2 left parenthesis straight z minus 3 right parenthesis over denominator 4 end fraction
rightwards double arrow fraction numerator straight x minus 3 over denominator negative 5 end fraction equals fraction numerator straight y minus left parenthesis negative 4 right parenthesis over denominator 7 end fraction equals fraction numerator straight z minus 3 over denominator 2 end fraction equals straight lambda
    Any point on the line is of the form:
    negative 5 straight lambda plus 3 comma space space 7 straight lambda minus 4 comma space space 2 straight lambda plus 3
    Thus, the vector equation is of the form:
    straight r with rightwards arrow on top space equals straight a with rightwards arrow on top plus straight lambda straight b with rightwards arrow on top comma space where space straight a with rightwards arrow on top space is space the space position space vector space of space any space point
on space the space line space and space straight b with rightwards arrow on top space is space the space vector space parallel space to space the space line. space
Therefore comma space the space vector space equation space is
straight r with rightwards arrow on top equals space left parenthesis negative 5 straight lambda plus 3 right parenthesis straight i with hat on top plus open parentheses 7 straight lambda minus 4 close parentheses straight j with hat on top space plus space left parenthesis 2 straight lambda plus 3 right parenthesis straight k with hat on top
space space rightwards double arrow space straight r with rightwards arrow on top equals negative 5 straight lambda straight i with hat on top plus 7 straight lambda straight j with hat on top plus 2 straight lambda straight k with hat on top plus 3 straight i with hat on top minus 4 straight j with hat on top plus 3 straight k with hat on top
space space space space rightwards double arrow straight r with rightwards arrow on top equals 3 straight i with hat on top minus 4 straight j with hat on top plus 3 straight k with hat on top plus straight lambda open parentheses negative 5 straight i with hat on top plus 7 straight j with hat on top plus 2 straight k with hat on top close parentheses

    Question 572
    CBSEENMA12035698

    If space straight a with rightwards arrow on top space and space straight b with rightwards arrow on top space are space perpendicular space vectors comma space open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar space equals space 13 space and space open vertical bar straight a with rightwards arrow on top close vertical bar space equals 5 space and space find space the space value space of space open vertical bar straight b with rightwards arrow on top close vertical bar.

    Solution

    Given that straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are two perpendiculars vectors.
    Thus, straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0
    Also given that, open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar equals 13 space and space open vertical bar straight a with rightwards arrow on top close vertical bar equals 5.
    We need to find the value of straight b with rightwards arrow on top.
    Consider open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar squared colon
    open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar squared space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus 2 open vertical bar straight a with rightwards arrow on top. straight b with rightwards arrow on top close vertical bar plus open vertical bar straight b with rightwards arrow on top close vertical bar squared
13 squared space equals space 5 squared plus 2 cross times 0 plus open vertical bar straight b with rightwards arrow on top close vertical bar squared
169 space equals 25 plus open vertical bar straight b with rightwards arrow on top close vertical bar squared
open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals 169 minus 25
open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals 144
straight b with rightwards arrow on top space equals space 12

    Question 573
    CBSEENMA12035700

    Show that the four points A, B, C and D with position vectors
    4 straight i with hat on top plus 5 straight j with hat on top plus straight k with hat on top comma negative straight j with hat on top minus straight k with hat on top comma space 3 straight i with hat on top plus 9 straight j with hat on top plus 4 straight k with hat on top space and space 4 left parenthesis negative straight i with hat on top plus straight j with hat on top plus straight k with hat on top right parenthesis respectively are coplanar.

    Solution

    Given position vectors of four points A, B, C and D are:
    OA with rightwards arrow on top space equals space 4 straight i with hat on top minus 5 straight j plus straight k
OB with rightwards arrow on top space equals negative straight j minus straight k
OC with rightwards arrow on top equals 3 straight i with hat on top plus 9 straight j plus 4 straight k
OD with rightwards arrow on top equals space 4 open parentheses negative straight i with hat on top plus straight j plus straight k close parentheses
    These points are coplanar, if the vectors, AB with rightwards arrow on top comma space AC with rightwards arrow on top space and space AD with rightwards arrow on top are coplanar. 
    AB with rightwards arrow on top space equals OB with rightwards arrow on top minus OA with rightwards arrow on top
equals negative straight j minus straight k minus open parentheses 4 straight i with hat on top plus 5 straight j plus straight k close parentheses equals negative 4 straight i with hat on top minus 6 straight j minus 2 straight k
AC with rightwards arrow on top equals OC with rightwards arrow on top minus OA with rightwards arrow on top
equals 3 straight i with hat on top plus 9 straight j plus 4 straight k minus open parentheses 4 straight i with hat on top plus 5 straight j plus straight k close parentheses equals negative straight i with hat on top plus 4 straight j plus 3 straight k
AB with rightwards arrow on top space equals OD with rightwards arrow on top minus OA with rightwards arrow on top
equals 4 open parentheses negative straight i with hat on top plus straight j plus straight k close parentheses minus open parentheses 4 straight i with hat on top plus 5 straight j plus straight k close parentheses equals negative 8 straight i with hat on top minus straight j plus 3 straight k
    These vectors are coplanar if and only if, they can be expressed as a linear combination of other two. 
    So Let
    AB with rightwards arrow on top space equals space straight x AC with rightwards arrow on top space plus straight y AD with rightwards arrow on top
rightwards double arrow space minus 4 straight i with hat on top minus 6 straight j minus 2 straight k equals straight x open parentheses negative straight i with hat on top plus 4 straight j plus 3 straight k close parentheses plus straight y open parentheses negative 8 straight i with hat on top minus straight j with hat on top plus 3 straight k with hat on top close parentheses
rightwards double arrow space minus 4 straight i with hat on top minus 6 straight j with hat on top minus 2 straight k with hat on top equals space open parentheses negative straight x minus 8 straight y close parentheses straight i with hat on top plus left parenthesis 4 straight x minus straight y right parenthesis straight j with hat on top plus left parenthesis 3 straight x plus 3 straight y right parenthesis straight k with hat on top
    Comparing the coefficients, we have, 
    negative straight x minus 8 straight y equals negative 4 semicolon space space 4 straight x minus straight y equals negative 6 semicolon space space 3 straight x plus 3 straight y equals negative 2
Thus comma space solving space the space first space two space equations comma space space we space get
straight x equals fraction numerator negative 4 over denominator 3 end fraction space and space straight y space equals 2 over 3
    These values of x and y satisfy the equation  3x + 3y = -2.
    Hence the vectors are coplanar. 

    Question 575
    CBSEENMA12035716

    Find the distance of the point (2, 12, 5) from the point of intersection of the line 
    straight r with rightwards arrow on top equals 2 straight i with hat on top minus 4 straight j with hat on top plus 2 straight k with hat on top plus straight lambda open parentheses 3 straight i with hat on top plus 4 straight j with hat on top plus 2 straight k with hat on top close parentheses space and space the space plane space straight r with rightwards arrow on top. open parentheses straight i with hat on top minus 2 straight j with hat on top plus straight k with hat on top close parentheses equals 0.

    Solution

    Any point in the line is
    2 plus 3 straight lambda comma space minus 4 plus 4 straight lambda comma space space 2 plus 2 straight lambda
    The vector equation of the plane is given as
    straight r with rightwards arrow on top. space open parentheses straight i with hat on top minus 2 straight j close parentheses plus straight k right parenthesis space equals space 0
Thus space the space cartesian space equation space of space the space plane space is space straight x minus 2 straight y plus straight z equals space 0
Since space the space point space lies space in space the space plane
left parenthesis 2 plus 3 straight lambda right parenthesis 1 plus left parenthesis negative 4 plus 4 straight lambda right parenthesis thin space left parenthesis negative 2 right parenthesis plus left parenthesis 2 plus 2 straight lambda right parenthesis 1 space equals 0
rightwards double arrow space 2 plus 8 plus 2 plus 3 straight lambda minus 8 straight lambda plus 2 straight lambda equals 0
rightwards double arrow 12 minus 3 straight lambda equals 0
rightwards double arrow 12 equals space 3 straight lambda
rightwards double arrow straight lambda equals 4
    Thus, the point of intersection of the line and the plane is:
    2 plus 3 cross times 4 comma space minus 4 plus 4 cross times 4 comma space space 2 plus 2 cross times 4
    rightwards double arrow 14 comma space 12 comma space 10
    Distance between (2, 12, 5) and (14, 12, 10) is:
    straight d equals square root of left parenthesis 14 minus 2 right parenthesis squared plus left parenthesis 12 minus 12 right parenthesis squared plus left parenthesis 10 minus 5 right parenthesis squared end root
rightwards double arrow straight d equals space square root of 144 plus 25 end root
rightwards double arrow space straight d equals square root of 169
rightwards double arrow straight d space equals space 13 space units

    Question 576
    CBSEENMA12035730

    If a unit vector straight a with rightwards arrow on top space equals space straight x straight i with hat on top plus 2 straight j with hat on top minus straight z straight k with hat on top and straight b with rightwards arrow on top space equals space 3 straight i with hat on top minus straight y straight j with hat on top plus straight k with hat on top are two equal vectors, then write the value of x+y+z.

    Solution

    Given that straight a with rightwards arrow on top equals straight x straight i with hat on top plus 2 straight j with hat on top minus straight z straight k with hat on top and straight b with rightwards arrow on top equals 3 straight i with hat on top minus straight y straight j with hat on top plus straight k with hat on top are equal vectors.
    therefore space straight x straight i with hat on top plus 2 straight j with hat on top minus straight z straight k with hat on top space equals space 3 straight i with hat on top minus straight y straight j with hat on top plus straight k with hat on top
rightwards double arrow straight x equals space 3 comma space space straight y space equals space minus 2 comma space space straight z equals space minus 1
therefore space space straight x plus straight y plus straight z space equals space 3 plus left parenthesis negative 2 right parenthesis plus left parenthesis negative 1 right parenthesis space equals space 0

    Question 578
    CBSEENMA12035746

    If straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are two vectors such that open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar equals open vertical bar straight a with rightwards arrow on top close vertical bar comma then prove that vector 2 straight a with rightwards arrow on top plus straight b with rightwards arrow on top is perpendicular to vector straight b with rightwards arrow on top.

    Solution
    open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar equals open vertical bar straight a with rightwards arrow on top close vertical bar
space rightwards double arrow space space open vertical bar straight a with rightwards arrow on top plus straight b with rightwards arrow on top close vertical bar squared space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared
space rightwards double arrow space space space open vertical bar straight a with rightwards arrow on top close vertical bar squared plus 2 straight a with rightwards arrow on top. straight b with rightwards arrow on top plus open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space open vertical bar straight a with rightwards arrow on top close vertical bar squared
space rightwards double arrow 2 straight a with rightwards arrow on top. straight b with rightwards arrow on top plus open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals space 0 space space space space... left parenthesis 1 right parenthesis
    Now comma space open parentheses 2 straight a with rightwards arrow on top plus straight b with rightwards arrow on top close parentheses. space left parenthesis straight b with rightwards arrow on top right parenthesis space equals space 2 straight a with rightwards arrow on top. straight b with rightwards arrow on top plus straight b with rightwards arrow on top. straight b with rightwards arrow on top space equals space 2 straight a with rightwards arrow on top. straight b with rightwards arrow on top plus open vertical bar straight b with rightwards arrow on top close vertical bar squared space equals 0       [Using (1)]
    We know that if the dot product of two vectors is zero, then either of the two vectors is zero or the vectors are perpendicular to each other.
    Thus, 2 straight a with rightwards arrow on top plus straight b with rightwards arrow on top is perpendicular to straight b with rightwards arrow on top.
    Question 579
    CBSEENMA12035747

    Find the coordinates of the point, where the line fraction numerator straight x minus 2 over denominator 3 end fraction equals fraction numerator straight y plus 1 over denominator 4 end fraction equals fraction numerator straight z minus 2 over denominator 2 end fraction intersects the plane straight x minus straight y plus straight z minus 5 space equals space 0. Also find the angle between the line and the plane. 

    Solution

    The equation of the given line is fraction numerator straight x minus 2 over denominator 3 end fraction equals space fraction numerator straight y plus 1 over denominator 4 end fraction equals fraction numerator straight z minus 2 over denominator 2 end fraction space space... left parenthesis 1 right parenthesis
    Any point on the given line is left parenthesis 3 straight lambda plus 2 comma space 4 straight lambda minus 1 comma space 2 straight lambda plus 2 right parenthesis.
    If this point lies on the given plane x - y + z - 5 = 0, then
    3 straight lambda plus 2 minus left parenthesis 4 straight lambda minus 1 right parenthesis plus 2 straight lambda plus 2 minus 5 space equals space 0
rightwards double arrow straight lambda space equals space 0
    Putting straight lambda space equals space 0 in left parenthesis 3 straight lambda plus 2 comma space 4 straight lambda minus 1 comma space 2 straight lambda plus 2 right parenthesis comma we get the point of intersection of the given line and the plane is (2, -1, 2).
    Let straight theta be the angle between the given line and the plane. 
    therefore space space sin space straight theta space equals space fraction numerator straight a with rightwards arrow on top. straight b with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top close vertical bar open vertical bar straight b with rightwards arrow on top close vertical bar end fraction space equals fraction numerator left parenthesis 3 straight i with rightwards arrow on top plus 4 straight j with rightwards arrow on top plus 2 stack straight k right parenthesis with rightwards arrow on top. left parenthesis straight i with rightwards arrow on top minus straight j with rightwards arrow on top plus straight k with rightwards arrow on top right parenthesis over denominator square root of 3 squared plus 4 squared plus 2 squared end root square root of 1 squared plus 1 squared plus 1 squared end root end fraction equals fraction numerator 3 minus 4 plus 2 over denominator square root of 29 square root of 3 end fraction equals fraction numerator 1 over denominator square root of 87 end fraction
rightwards double arrow straight theta space equals sin to the power of negative 1 end exponent open parentheses fraction numerator 1 over denominator square root of 87 end fraction close parentheses
    Thus, the angle between the given line and the given plane is sin to the power of negative 1 end exponent open parentheses fraction numerator 1 over denominator square root of 87 end fraction close parentheses.

    Question 580
    CBSEENMA12035748

    Find the vector equation of the plane which contains the line of intersection of the planes. straight r with rightwards arrow on top. open parentheses straight i with hat on top plus 2 straight j with hat on top plus 3 straight k with hat on top close parentheses minus 4 space equals 0 and straight r with rightwards arrow on top. open parentheses 2 straight i with hat on top plus straight j with hat on top minus straight k with hat on top close parentheses plus 5 space equals 0 and which is perpendicular to the plane straight r with rightwards arrow on top. space open parentheses 5 straight i with hat on top plus 3 straight j with hat on top minus 6 straight k with hat on top close parentheses plus 8 space equals space 0

    Solution

    The equation of the given planes are
    straight r with rightwards arrow on top. open parentheses straight i with hat on top plus 2 straight j plus 3 straight k with hat on top close parentheses minus 4 space equals space 0 space space... left parenthesis 1 right parenthesis
straight r with rightwards arrow on top. left parenthesis 2 straight i with hat on top plus straight j with hat on top minus straight k with hat on top right parenthesis plus 5 space equals space 0 space space space... left parenthesis 2 right parenthesis
    The equation of the plane passing through the intersection of the planes (1) and (2) is
    open square brackets straight r with rightwards arrow on top. open parentheses straight i with hat on top plus 2 straight j with hat on top plus 3 straight k with hat on top close parentheses minus 4 close square brackets plus straight lambda open square brackets straight r with rightwards arrow on top. open parentheses 2 straight i with hat on top plus straight j with hat on top minus straight k with hat on top close parentheses plus 5 close square brackets equals 0
space space rightwards double arrow space space straight r with rightwards arrow on top open square brackets open parentheses 1 plus 2 straight lambda close parentheses straight i with hat on top plus left parenthesis 2 plus straight lambda right parenthesis straight j with hat on top plus left parenthesis 3 minus straight lambda right parenthesis straight k with hat on top close square brackets space equals space 4 minus 5 straight lambda space space space... left parenthesis 3 right parenthesis
    Given that plane (3) is perpendicular to the plane straight r with rightwards arrow on top. open parentheses 5 straight i with hat on top plus 3 straight j with hat on top minus 6 straight k with hat on top close parentheses plus 8 space equals space 0
    open parentheses 1 plus 2 straight lambda close parentheses cross times 5 plus left parenthesis 2 plus straight lambda right parenthesis cross times 3 plus left parenthesis 3 minus straight lambda right parenthesis cross times left parenthesis negative 6 right parenthesis space equals space 0
rightwards double arrow space space 19 straight lambda minus 7 space equals space 0
rightwards double arrow space space space straight lambda space equals space 7 over 19
Putting space straight lambda space equals space 7 over 19 space in space left parenthesis 3 right parenthesis comma space we space get
    straight r with rightwards arrow on top open square brackets open parentheses 1 plus 14 over 19 close parentheses straight i with hat on top plus open parentheses 2 plus 7 over 19 close parentheses straight j with hat on top plus open parentheses 3 minus 7 over 19 close parentheses straight k with hat on top close square brackets space equals space 4 minus 35 over 19
rightwards double arrow space space straight r with rightwards arrow on top. open parentheses 33 over 19 straight i with hat on top plus 45 over 19 straight j with hat on top plus 50 over 19 straight k with hat on top close parentheses space equals space 41 over 19
rightwards double arrow space space straight r with rightwards arrow on top. open parentheses 33 straight i with hat on top plus 45 straight j with hat on top plus 50 straight k with hat on top close parentheses space equals space 41
    This is the equation of the required line. 

    Question 581
    CBSEENMA12035756

    Find the vector equation of the plane passing through three points with position vectors straight i with hat on top plus straight j with hat on top minus 2 straight k with hat on top comma space 2 straight i with hat on top minus straight j with hat on top plus straight k with hat on top space and space straight i with hat on top plus 2 straight j with hat on top plus straight k with hat on top. Also, find the coordinates of the point of intersection of this plane and the line straight r with rightwards arrow on top space equals 3 straight i with hat on top minus straight j with hat on top minus straight k with hat on top plus straight lambda open parentheses 2 straight i with hat on top minus 2 straight j with hat on top plus straight k with hat on top close parentheses.

    Solution

    Let the position vectors of the three points be, 
    straight a with rightwards arrow on top equals straight i with hat on top plus straight j with hat on top minus 2 straight k with hat on top comma space space straight b with rightwards arrow on top equals 2 straight i with hat on top minus straight j with hat on top plus straight k with hat on top space space and space straight c with rightwards arrow on top equals straight i with hat on top plus 2 straight j with hat on top plus straight k with hat on top.
    So, the equation of the plane passing through the point straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top space is
    open parentheses straight r with rightwards arrow on top minus straight a with rightwards arrow on top close parentheses. open square brackets left parenthesis straight b with rightwards arrow on top. negative straight c with rightwards arrow on top right parenthesis space cross times space left parenthesis straight c with rightwards arrow on top minus straight a with rightwards arrow on top right parenthesis close square brackets space equals space 0
rightwards double arrow space space open square brackets straight r with rightwards arrow on top. open parentheses straight i with hat on top plus straight j with hat on top minus 2 straight k with hat on top close parentheses close square brackets. space open square brackets left parenthesis straight i with hat on top minus 3 straight j with hat on top right parenthesis cross times left parenthesis straight j with hat on top plus 3 straight k with hat on top right parenthesis close square brackets equals 0
rightwards double arrow space open square brackets straight r with rightwards arrow on top minus open parentheses straight i with hat on top plus straight j with hat on top minus 2 straight k with hat on top close parentheses close square brackets. space open parentheses straight k with hat on top minus 3 straight j with hat on top minus 9 straight i with hat on top close parentheses equals 0
rightwards double arrow straight r with rightwards arrow on top. left parenthesis negative 9 straight i with hat on top minus 3 straight j with hat on top plus straight k with hat on top right parenthesis plus 14 space equals space 0
rightwards double arrow space straight r with rightwards arrow on top. open parentheses 9 straight i with hat on top plus 3 straight j with hat on top minus straight k with hat on top close parentheses equals 14 space space space space space space space space space... left parenthesis 1 right parenthesis
    So, the vector equation of the required plane is straight r with rightwards arrow on top. space open parentheses 9 straight i with hat on top plus 3 straight j with hat on top minus straight k with hat on top close parentheses space equals space 14.
    The equation of the given line is straight r with rightwards arrow on top space equals space open parentheses 3 straight i with hat on top minus straight j with hat on top minus straight k with hat on top close parentheses plus straight lambda left parenthesis 2 straight i with hat on top minus 2 straight j with hat on top plus straight k with hat on top right parenthesis.
    Position vector of any point on the given line is
    straight r with rightwards arrow on top space equals space left parenthesis 3 plus 2 straight lambda right parenthesis straight i with hat on top plus left parenthesis negative 1 minus 2 straight lambda right parenthesis straight j with hat on top plus left parenthesis negative 1 plus straight lambda right parenthesis straight k with hat on top   ....(2)
    The point (2) lies on plane (1) if, 
    open square brackets left parenthesis 3 plus 2 straight lambda right parenthesis straight i with hat on top plus left parenthesis negative 1 minus 2 straight lambda right parenthesis straight j with hat on top plus left parenthesis negative 1 plus straight lambda right parenthesis straight k with hat on top close square brackets. left parenthesis 9 straight i with hat on top plus 3 straight j with hat on top minus straight k with hat on top right parenthesis space equals space 14
rightwards double arrow space space 9 left parenthesis 3 plus 2 straight lambda right parenthesis plus 3 left parenthesis negative 1 minus 2 straight lambda right parenthesis minus left parenthesis negative 1 plus straight lambda right parenthesis equals space 14
rightwards double arrow space space 11 straight lambda plus 25 space equals 14
rightwards double arrow space space straight lambda space equals negative 1
    Putting straight lambda equals negative 1 in (2), we have
    straight r with rightwards arrow on top equals left parenthesis 3 plus 2 straight lambda right parenthesis straight i with hat on top plus left parenthesis negative 1 minus 2 straight lambda right parenthesis straight j with hat on top plus left parenthesis negative 1 plus left parenthesis negative 1 right parenthesis right parenthesis straight k with hat on top
space space equals open parentheses 3 plus 2 left parenthesis negative 1 right parenthesis close parentheses straight i with hat on top plus left parenthesis negative 1 minus 2 left parenthesis negative 1 right parenthesis right parenthesis straight j with hat on top plus left parenthesis negative 1 plus left parenthesis negative 1 right parenthesis right parenthesis straight k with hat on top
equals straight i with hat on top plus straight j with hat on top minus 2 straight k with hat on top
    Thus, the position vector of the point of intersection of the given line and plane (1) is 
    straight i with hat on top plus straight j with hat on top minus 2 straight k with hat on top and its co-ordinates are (1, 1, -2).

    Question 582
    CBSEENMA12035779

    Prove that x2 – y2 = c(x2 + y2)2 is the general solution of the differential equation (x3 – 3xy2)dx = (y3 – 3x2y) dy, where C is a parameter.

    Solution

    Given equation is
    (x3 – 3xy2)dx = (y3 – 3x2y) dy
    rightwards double arrow dy over dx space equals space fraction numerator straight x cubed minus 3 xy squared over denominator straight y cubed minus 3 straight x squared straight y end fraction
    which is a homogeneous equation.
    Therefore substituting y = vx
    We have,
    dy over dx space equals space straight v space plus straight x. dv over dx
straight v plus straight x. dv over dx space equals space fraction numerator straight x cubed minus 3 straight x. straight v squared straight x squared over denominator straight v cubed straight x cubed minus 3 straight x squared. vx end fraction
straight v plus straight x. dv over dx space equals space fraction numerator 1 minus 3 straight v squared over denominator straight v cubed minus 3 straight v end fraction
straight x. dv over dx space equals space fraction numerator begin display style 1 minus 3 straight v squared end style over denominator begin display style straight v cubed minus 3 straight v end style end fraction space minus straight V
straight x. dv over dx space equals space fraction numerator begin display style 1 minus 3 straight v squared space minus straight v to the power of 4 space plus 3 straight v squared end style over denominator straight v cubed minus 3 straight v end fraction
fraction numerator straight v cubed minus 3 straight v over denominator 1 minus straight v to the power of 4 end fraction. dv space equals 1 over straight x. dx
    Integrating the equation both sides, 
    log space straight x space equals space integral fraction numerator straight v cubed minus 3 straight v over denominator 1 minus straight v to the power of 4 end fraction dv
rightwards double arrow space log space straight C apostrophe space plus log space straight x space equals space integral fraction numerator straight v cubed over denominator 1 minus straight v to the power of 4 end fraction. dv minus 3. integral fraction numerator straight v over denominator 1 minus straight v to the power of 4 end fraction. dv
log space straight C apostrophe straight x space equals space straight I subscript 1 minus 3. straight I subscript 2.......... space left parenthesis 1 right parenthesis space where space straight C space is space an space integration space constant
straight I subscript 1 space equals space integral fraction numerator straight v cubed over denominator 1 minus straight v to the power of 4 end fraction. dv
let space 1 minus straight v to the power of 4 space equals space straight t
rightwards double arrow space minus 4 straight v cubed. dv space equals space dt
straight I subscript 1 space equals space integral 1 over straight t. open parentheses fraction numerator dt over denominator negative 4 end fraction close parentheses space equals space minus 1 fourth. log space straight t
straight I subscript 1 space equals space minus 1 fourth space lof space left parenthesis 1 minus straight v to the power of 4 right parenthesis space.... left parenthesis 2 right parenthesis
straight I subscript 2 space equals space integral fraction numerator straight v over denominator 1 minus straight v to the power of 4 end fraction. dv
let space straight v squared space equals space straight t
rightwards double arrow space 2 straight v. dv space equals space dt
straight I subscript 2 space equals space integral fraction numerator 1 over denominator 1 minus straight t squared end fraction. open parentheses dt over 2 close parentheses space equals space 1 fourth. log fraction numerator 1 plus straight t over denominator 1 minus straight t end fraction
straight I subscript 2 space equals space 1 fourth. log space open parentheses fraction numerator 1 plus straight v squared over denominator 1 minus straight v squared end fraction close parentheses
    thus substituting the values of I1 and I2
    log space straight C apostrophe straight x space equals space minus 1 fourth. log space left parenthesis 1 minus straight v to the power of 4 right parenthesis minus 3 over 4. log space open parentheses fraction numerator 1 plus straight v squared over denominator 1 minus straight v squared end fraction close parentheses
log space straight C apostrophe straight x space equals space minus space 1 fourth. space open square brackets log space open parentheses 1 minus straight v to the power of 4 close parentheses minus 3 over 4. log open parentheses fraction numerator 1 plus straight v squared over denominator 1 minus straight v squared end fraction close parentheses cubed close square brackets
log space straight C apostrophe straight x space equals space minus 1 fourth. open square brackets log space open parentheses 1 minus straight v to the power of 4 close parentheses. open parentheses fraction numerator 1 plus straight v squared over denominator 1 minus straight v squared end fraction close parentheses cubed close square brackets
log space straight C apostrophe straight x space equals space minus 1 fourth. space log space open square brackets left parenthesis 1 minus straight v squared right parenthesis left parenthesis 1 plus straight v squared right parenthesis fraction numerator left parenthesis 1 plus straight v squared right parenthesis cubed over denominator left parenthesis 1 minus straight v squared right parenthesis cubed end fraction close square brackets
log space straight C apostrophe straight x space equals space 1 fourth. log space open square brackets fraction numerator left parenthesis 1 plus straight v squared right parenthesis to the power of 4 over denominator left parenthesis negative straight v squared right parenthesis squared end fraction close square brackets
space equals space log space open square brackets fraction numerator left parenthesis 1 plus straight v squared right parenthesis to the power of 4 over denominator left parenthesis 1 minus straight v squared right parenthesis squared end fraction close square brackets to the power of 1 divided by 4 end exponent
space equals space log space open square brackets fraction numerator left parenthesis 1 minus straight v squared right parenthesis to the power of 1 divided by 2 end exponent over denominator left parenthesis 1 plus straight v squared right parenthesis end fraction close square brackets
rightwards double arrow straight C apostrophe straight x space equals space fraction numerator left parenthesis 1 minus straight v squared right parenthesis to the power of 1 divided by 2 end exponent over denominator left parenthesis 1 plus straight v squared right parenthesis end fraction
straight C apostrophe straight x space equals space fraction numerator open parentheses 1 minus begin display style straight y squared over straight x squared end style close parentheses to the power of 1 divided by 2 end exponent over denominator 1 plus begin display style straight y squared over straight x squared end style end fraction
straight C apostrophe straight x space equals space fraction numerator begin display style fraction numerator left parenthesis straight x squared minus straight y squared right parenthesis to the power of 1 divided by 2 end exponent over denominator straight x end fraction end style over denominator left parenthesis straight x squared plus straight y squared right parenthesis divided by straight x squared end fraction space equals space fraction numerator left parenthesis straight x squared minus straight y squared right parenthesis to the power of 1 divided by 2 end exponent over denominator left parenthesis straight x squared plus straight y squared right parenthesis end fraction
straight C apostrophe left parenthesis straight x squared plus straight y squared right parenthesis space equals space left parenthesis straight x squared minus straight y squared right parenthesis
squaring space both space sides space
straight C apostrophe left parenthesis straight x squared plus straight y squared right parenthesis squared space equals space left parenthesis straight x squared minus straight y squared right parenthesis

    Question 583
    CBSEENMA12035780
    Question 584
    CBSEENMA12035781

    Let space straight a with rightwards arrow on top space equals space straight i with hat on top space plus straight j with hat on top space plus stack straight k comma with hat on top space
straight b with rightwards arrow on top space equals space straight i with hat on top space and
straight c with rightwards arrow on top space equals space straight c subscript 1 straight i with hat on top space plus straight c subscript 2 straight j with hat on top space plus straight c subscript 3 straight k with hat on top space space then
    a) Let c1 = 1 and c2 = 2, find c3 which makes straight a with rightwards arrow on top space comma straight b with rightwards arrow on top space and space straight c with rightwards arrow on top coplanar.
    b) If c2 = –1 and c3 = 1, show that no value of c1 can make straight a with rightwards arrow on top space comma straight b with rightwards arrow on top space and space straight c with rightwards arrow on top coplanar.

    Solution
    straight a with rightwards arrow on top space equals space straight i with hat on top space plus straight j with hat on top plus straight k with hat on top comma
straight b with hat on top space equals space straight i with hat on top
straight c with hat on top space equals space straight c subscript 1 straight i with hat on top space plus space straight c subscript 2 straight j with hat on top space plus straight c subscript 3 straight k with hat on top
    then,
    a) c1 = 1 and c2 = 2,
    straight c with hat on top space equals space straight c subscript 1 straight i with hat on top space plus space straight c subscript 2 straight j with hat on top space plus straight c subscript 3 straight k with hat on top
    For vectors to be coplanar scalar triple product should be equal to zero.
    therefore space straight a with rightwards arrow on top space left parenthesis straight b with rightwards arrow on top space straight x space straight c with rightwards arrow on top right parenthesis space equals space 0
rightwards double arrow space left parenthesis straight i with hat on top space plus straight j with hat on top space plus straight k with hat on top right parenthesis. space left square bracket straight i with hat on top space straight x left parenthesis straight i with hat on top space plus 2 straight j with hat on top space plus straight c subscript 3 straight k with hat on top right parenthesis right square bracket space equals space 0
rightwards double arrow space left parenthesis straight i with hat on top space plus straight j with hat on top space plus straight k with hat on top right parenthesis. left parenthesis negative straight c subscript 3 straight j with hat on top space plus 2 straight k with hat on top right parenthesis space equals space 0
rightwards double arrow space 0 minus straight c subscript 3 space plus 2 space equals 0
rightwards double arrow straight C subscript 3 space equals space 2
    b) c2 = –1 and c3 = 1
    straight c with rightwards arrow on top space equals space straight c subscript 1 straight i with hat on top minus straight j with hat on top plus space straight k with hat on top
Let space straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top space be space coplanar.
For space vectors space to space be space coplanar space scalar space triple space product space should space be space equal space to space zero.
therefore space straight a with rightwards arrow on top left parenthesis straight b with rightwards arrow on top space straight x space straight c with rightwards arrow on top right parenthesis space equals space 0
left parenthesis straight i with hat on top space plus straight j with hat on top plus straight k with hat on top right parenthesis. open square brackets straight i with hat on top space straight x space left parenthesis straight c subscript 1 straight i with hat on top space minus straight j with hat on top plus straight k with hat on top close square brackets
space open square brackets straight i with hat on top space straight x space left parenthesis straight c subscript 1 straight i with hat on top space minus straight j with hat on top plus straight k with hat on top close square brackets space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row 1 0 0 row cell straight c subscript 1 end cell cell negative 1 end cell 1 end table close vertical bar
equals space straight i with hat on top space left parenthesis 0 minus 0 right parenthesis minus straight j with hat on top space left parenthesis 1 minus 0 right parenthesis space plus straight k with hat on top left parenthesis negative 1 minus 0 right parenthesis
space equals negative straight j with hat on top minus straight k with hat on top
    Question 585
    CBSEENMA12035791

    Using integration, find the area of region bounded by the triangle whose vertices are (–2, 1), (0, 4) and (2, 3).

    Solution

    the vertices of the triangle be A(–2, 1), B(0, 4) and C(2, 3).
    Equation of line segment AB is
    Equation space of space line space segment space AB space is
left parenthesis straight y minus 1 right parenthesis space equals space fraction numerator left parenthesis 4 minus 1 right parenthesis over denominator left parenthesis 0 plus 2 right parenthesis end fraction left parenthesis straight x plus 2 right parenthesis
rightwards double arrow space straight y space equals space fraction numerator 3 left parenthesis straight x plus 2 right parenthesis over denominator 2 end fraction space plus 1
rightwards double arrow space straight y space equals fraction numerator space 3 straight x space plus space 6 plus 2 over denominator 2 end fraction
rightwards double arrow space straight y space equals space fraction numerator 3 straight x plus 8 over denominator 2 end fraction
Equation space of space line space segment space BC space is
left parenthesis straight y minus 4 right parenthesis space equals space fraction numerator left parenthesis 3 minus 4 right parenthesis over denominator left parenthesis 2 minus 0 right parenthesis end fraction left parenthesis straight X minus 0 right parenthesis
rightwards double arrow space straight Y space equals space minus space 1 half space straight x space plus 4
Equation space of space line space segment space AC space is
left parenthesis straight y minus 3 right parenthesis space equals space fraction numerator left parenthesis 1 minus 3 right parenthesis over denominator left parenthesis negative 2 minus 2 right parenthesis end fraction left parenthesis straight X minus 2 right parenthesis
rightwards double arrow space straight Y space equals space space straight x over 2 space plus 2

    AL, BO and CM are drawn perpendicular to x-axis.
    It can be observed in the following figure that,
    Area (ΔACB) = Area (ABOL) + Area (BOMCB) – Area (ALMCA)
    Area space left parenthesis ABOL right parenthesis space equals space integral subscript negative 2 end subscript superscript 0 open parentheses fraction numerator 3 straight x space plus 8 over denominator 2 end fraction close parentheses space dx
space equals space integral subscript negative 2 end subscript superscript 0 space open parentheses fraction numerator 3 straight x over denominator 2 end fraction plus 4 close parentheses space dx
space equals fraction numerator 3 straight x squared over denominator 4 end fraction space plus right enclose 4 straight x end enclose subscript negative 2 end subscript superscript 0
space equals space left parenthesis 0 space plus space 0 right parenthesis minus open parentheses 12 over 4 minus 8 close parentheses
space equals space 5 space sq space units
Area space left parenthesis BOMCB right parenthesis space equals space integral subscript 0 superscript 2 open parentheses 1 half straight x space plus space 4 close parentheses dx
space equals space right enclose space open parentheses negative straight x squared over 4 plus 4 straight x squared close parentheses end enclose subscript 0 superscript 2
space equals space left parenthesis negative 1 plus space 8 right parenthesis minus left parenthesis 0 space plus space 0 right parenthesis
space equals space 7 space sq space units
Area space left parenthesis ALMCA right parenthesis space equals space integral subscript negative 2 end subscript superscript 2 space open parentheses straight x over 2 plus 2 close parentheses dx
space equals space space equals space right enclose space open parentheses straight x squared over 4 plus 2 straight x close parentheses end enclose subscript negative 2 end subscript superscript 2
space equals space left parenthesis 1 plus 4 right parenthesis minus left parenthesis 1 minus 4 right parenthesis
space equals space 8 space sq space units
space Required space area space equals space 4 space units

    Question 586
    CBSEENMA12035793

    Find the magnitude of each of the two vectors a and b, having the same magnitude such that the angle between them is 60o and their scalar product is 9/2.

    Solution

    Given that,

    |a| = |b|θ = 60° and a .b = 92

    As, we know that, 

    a. b = |a||b| cos θwhere θ is the angle between a and b 92 = |a|2 cos 60o ( |a| = |b|) 92 = |a|2 . 12 9 = |a|2 |a| = 3

    Hence, the magnitude of each of the vectors a and b is 3.

    Question 587
    CBSEENMA12035801

    If θ is the angle between two vectors i^ - 2j^ + 3k^ and 3i^ - 2j^ + k^ find sin θ.

    Solution

    a = i^ - 2j^ + 3k^b = 3i^ - 2j^ + k^a x b = i^j^k^1-233-21 = (4)i^ + 8j^ + 4k^|a x b| = (4)2 + (8)2 + (4)2  = 16 + 64 + 16 = 96= 46|a| = 12 + (-2)2 + 32 = 14|b| = 32 + (-2)2 + 12 = 14 |a x b| = |a||b| sin  θwhere θ is the angle between a and b sin θ = 461414 = 4614 = 276sin θ = 276

    Question 588
    CBSEENMA12035814

    Let a = 4i^ + 5j^ - k^ , b = i^ - 4j^ + 5k^ and c = 3i^ + j^- k^. Find a vector d which perpendicular to both  c and b and d. a = 21

    Solution

    Since d is perpendicular to both c and b, therefore, if is parallel to c x b

     d = λ (c x b) = λ i^j^k^31-11-45 = λ (5-4)i^ - (15 + 1)j^ + (-12-1) k^ = λ i^ - 16j^ -13k^ Given thatd.a = 21λi^ - 16 j^ - 13k^.4 i^ + 5j^-k^ = 21λ (4 -80 + 13) = 21λ = 21-63 = - 13 d = 13i^ - 16 j^ - 13 k^ = -13i^ + 163j^ + 133k^

    Question 589
    CBSEENMA12035834

    Find a unit vector in the direction of  a = 3i ^ - 2j^ + 6k

    Solution

    The unit vector a^ in the direction of a is given by aaa^ = 3i^ - 2j^ + 6k^32 + (-2)2 + 62   = 3i^ - 2j^ + 6k^9+ 4 + 36  = 3i^ - 2j^ + 6k^49  = 173i^ - 2j^ + 6k^ =  37i^ - 27j^ + 67k^

    Question 590
    CBSEENMA12035835

    Find the angle between the vectors a = i^ - j^ + k^    and   b = 1^ + j^ - k^ 

    Solution

    a = i^ - j^ + k^b = i^ + j^ - k^Now,  a.b= a b cosθWhere θ is the angle between  a  and  b;  also  0 θ  π i^ - j^ + k^ .  i^ + j^ - k^ =   11 + ( - 1 )2 + 12   11 + ( - 1 )2 + 12  cosθ1 . 1 + (-1) . 1 + 1 . (-1) = 3 . 3 cosθ1 - 1 - 1 = 3cosθ-1 =  3cosθcosθ = -13   θ =  cos-1-13

    Question 591
    CBSEENMA12035836

    For what value of λ are the vectors  a = 2i^ + λ j^ + k^  and  b = i^ - 2j^ -3k^  are perpendicular to each other?

    Solution

    a = 2i^ + λ j^ + k^b = i^ - 2j^ + 3k^If  a and  b are perpendicular to each other, then a.b must be 0.a.b = 2i^ + λ j^ + k^ .  i^ - 2j^ + 3k^     0 = 2 . 1 + λ . (-2) + 1 . 3    0 = 2 - 2λ + 3  2λ = 5  λ = 52Thus, the value of  λ is  52

    Question 592
    CBSEENMA12035848

    If a = i^ + j^ + k^   and   b = j^ - k^,  find a vector  c  such that a × c = band a.c = 3

    Solution

    Let c = xi^ + yj^ + zk ^ a = i^ + j^ + k^ a x c = i^ j^ k^1 1  1x y z  a x c =  i^ ( z - y ) -  j^ ( z - x ) +  k^ ( y - x )    ...............(1)Now,  a x c = bb = j^ - k^                                                                ................(2)

     

    Comparing (1) and (2), we get:

    z - y = 0   z = y                                                   .............(3)z - x = -1                                                                 .............(4)y - x = -1                                                                 .............(5)

    Also, given that

    a.c =3 i^ + j^ + k^ . x i^ +y j^ +z k^ = 3x + y + z = 3

    Using (3), we get,  x + 2y = 3    .                  ...............(6)

    Adding (5) and (6), we get

     

    4y = 2  y = 23 z = 23       z=yfrom (6) we have,x = 3 - 2y x = 3 - 2 x 23 x = 9 - 43 x = 53 c = 53 i^ + 23 j^ + 23 k^.Thus the required vector  is c = 53 i^ + 23 j^ + 23 k^.

    Question 593
    CBSEENMA12035849

    If a + b + c  = 0   and  a = 3, b = 5  and c = 7,  show that the angle between a and b is 600.

    Solution

    a + b + c = 0   a + b = -ca + b . a + b = -c . -ca.a +2a. b + b.b   = c.ca2 + 2a b cosθ + b2 = c232 + 2 x 3 x 5 x cosθ + 52 = 72

    9 + 30 cosθ +25 = 4930 cosθ =15    cosθ = 12cosθ = cos60°  θ = 60°

    Hence proved.

     

    Question 594
    CBSEENMA12035867

    Find the projection of a on b if a. b =8  and  b = 2i^ + 6j^ + 3k^

    Solution

    Projection of a on b is given by a. b b       .......(1)Given  a. b = 8  and  b = 2i^ + 6j^ + 3k^b = 4 + 36 + 9 = 7

    Substituting value in (i) we get

    Projection of a on b = 87

    Question 595
    CBSEENMA12035868

    Write a unit vector in the direction of b = 2i^ + j^ + 2k^.

    Solution

    b = 2i^ + j^ + 2k^Unit vector in the direction of b is given by bbbb=  2i^ + j^ + 2k^9       = 13  2i^ + j^ + 2k^

    Question 596
    CBSEENMA12035869

    Write the value of p for which a = 3i^ + 2j^ + 9k^   and    b = i^+pj^ +3k^ are parallel vectors.

    Solution

    Two vectors a  and  b are parallel

    a = 3i^ + 2j^ + 9k^   and   b = i^ + pj^ + 3k^ a =λ bSo  3i^ + 2j^ + 9k^  = λ  i^ + pj^ + 3k^ 3i^ + 2j^ + 9k^  =λ i^ + p λ j^ + 3 λ k^ λ = 3,   p λ = 2   and  9 = 3 λ p = 23

    Question 597
    CBSEENMA12035880

    If a x b = c x d  and a x c = b x d, show that a - d is parallel to b - c, where a  d  and  b  c

    Solution

    Given: a x b = c x d    and   a x c = b x d       .........(i)To show ˙ a - d  is parallel to  b - ci.e.  a - d  x  b - c  = 0Consider   a - d  x  b - c  = a x  b - c   - d x  b - c = a x b -  a x c -  d x b +  d x c = c x d - b x d- d xb +  d x c       a x b = c x d and  a x c = b x d = c x d -b x d + b x d - c x d        d x c =- c x d  and   d xb = -b x d = 0therefore  ˙ a - d is parallel to   b - c.

    Question 598
    CBSEENMA12035901

    Write a vector of magnitude 15 units in the direction of vector  i^ - 2j^ + 2k

    Solution

    Unit vector along the direction of vector a,  a^ = a a Let   a = i^ - 2j^ + 2k a  =   1 2 +  - 2 2 +  2 2 = ±3i.e.   a^ = 13  i^ - 2j^ + 2 So, the vector whose magnitude is 15 and has direction along the vectori^ - 2j^ + 2k  is given by15 x 13  i^ - 2j^ + 2k = 5  i^ - 2j^ + 2k =  5i^ - 10j^ + 10k So the required vector is  5i^ - 10j^ + 10k

    Question 599
    CBSEENMA12035915

    Find the position vector of a point R which divides the line joining two points P and Q whose position vectors are   2a + b   and   a - 3b  respectively, externally in the ratio 1:2. Also, show that P is the midpoint of the line segment R.

    Solution

    Position vector of P is  2a +b Position vector of Q is  a -3b 

    Point R divides the lines segment PQ externally in a ratio of 1 : 2 .

    Position vector of R = 1 ( a -3b ) -2 (  2a +b ) 1 - 2                               =  a -3b - 4a - 2b1 - 2                               = 3a +5b

    Now, we need to show that P is the mid-point of RQ.

    So, position vector of P =  position vector of R +  position vector of Q2                                     =  3a + 5b  +  a - 3b 2                                     =   2a +b = Position vector  ( given )

    Hence proved.

    Question 600
    CBSEENMA12035939

    For what value of ‘a’ the vectors   2 i^  - 3 j^ + 4 k    and   a i^  + 6 j^  - 8 k   are collinear?

    Solution

    Two vectors  x  and  y  are collinear if  x = λ y,   where  λ  is a constant.Now, the vectors  2 i^ - 3 j^ + 4 k   and     a i^ + 6 j^ - 8 k    are collinear,  2 i^ - 3 j^ + 4 k   = λ  a i^ + 6 j^ - 8 k ,  where  λ  is a constant. 2 = λ a,    - 3 = 6 λ,     4 = - 8 λ Now,  - 3 = 6 λ      or      4 = -  8 λ      λ  = - 122 = λ a 2 = - 12 x a a = - 4

    Question 601
    CBSEENMA12035940

    Write the direction cosines of the vector  - 2 i^ + j^ - 5 k.

    Solution

    The direction cosines of the given vector  - 2 i^ + j^ - 5 k  is given by- 2  - 2 2 +  1 2 +  - 5 2 ,  1  - 2 2 +  1 2 +  - 5 2 ,  - 5  - 2 2 +  1 2 +  - 5 2  =  - 2 30,  1 30,  - 5 30 

    Question 602
    CBSEENMA12035955

    Find a unit vector perpendicular to each of the vector  a + b   and   a - b , where

      a = 3 i^ + 2 j^ + 2 k^   and    b =  i^ + 2 j^ - 2 k^.

    Solution

    a = 3 i^ + 2 j^ + 2 k^,     b =  i^ + 2 j^ - 2 k^. a  + b = 4 i^ + 4 j^       and      a  - b = 2 i^ + 4 k^   a  + b   x   a  - b  =  i^   j^  k^4    4      0 2     0     4  = i^  16  - j^  16  + k^  - 8                                           = 16 i^ - 16 j^ - 8 k^    a  + b   x   a  - b    =  162 + ( - 16 )2 + 64                                                      =  256 + 256 + 64                                                      =  576  = 24    

    So, the unit vector, perpendicular to each of the vectors  a + b    and    a + b is given by

    ±   a + b  x  a - b   a + b  x  a - b   = ± 16 i^ - 16 j^ - 8 k^24=  ± 2 i^ - 2 j^ -  k^3 =  ± 2 i^3  23 j^   13 k^

    Question 603
    CBSEENMA12035967

    Evaluate  1 - x   x  dx

    Solution

     1 - x   x  dx=    x - x32  dx =   x12- x32  dx= x32  32 - x52 52  +  C= 23  x32 -  23  x52  +  C

    Question 604
    CBSEENMA12035968

    Evaluate: 23 1x  dx

    Solution

    23 1x  dx  =  log x 23 = log 3 - log 2= log 32

    Question 605
    CBSEENMA12035970

    Find ' λ ' when the projection of  a = λ i^ + j^ + 4 k^    on    b = 2 i^ + 6 j^ + 3 k^  is  4  units.

    Solution

    Projection of  a  on  b  =   a .b  b   =  4   ( given )  λ i^ + j^ + 4 k^  .  2 i^ + 6 j^ + 3 k^  22 + 62 + 32  = 4 2 λ + 6 + 127  =  4 λ = 5.

    Question 606
    CBSEENMA12035971

    If a line has direction ratios 2,-1,-2 then what are its direction cosines?

    Solution

    The direction cosines are

    2 22 + ( - 1 )2 + ( - 2 )2,   - 1 22 + ( - 1 )2 + ( - 2 )2,   - 2 22 + ( - 1 )2 + ( - 2 )2= 23,  - 13,  - 23.

    Question 607
    CBSEENMA12035975

    Find the sum of the following vectors: 

    a = i^ - 2 j^ ,       b = 2 i^ - 3 j^ ,    c =2 i^ + 3 k^.

    Solution

    a + b + c =  i^ - 2 j^  +  2 i^ - 3 j^  +  2 i^ + 3 k^                     = 5 i^ - 5 j^  + 3 k^

    Question 608
    CBSEENMA12035977

    If  a ,  b ,   c  are three vectors such that  a  = 5,  b  = 12  and   c  = 13  and  a + b + c = 0  find the value of  a . b + b . c + c . a .

    Solution

    Considering dot product on both sides,

     a + b + c  .  a + b + c  = 0 . 0  a 2 +    b 2 +   c 2 + 2    a . b + b . c + c . a   = 0 52 + 122 + 132 + 2   a . b + b . c + c . a   = 0 2   a . b + b . c + c . a   = - 338    a . b + b . c + c . a   = - 3382=  - 169.

    Question 609
    CBSEENMA12035978

    Solve the following differential equation:

    2 x2 dydx - 2 x y + y2 = 0

    Solution

    Here,  2 x2 dydx - 2 x y + y2 = 0                      dydx =  2 x y - y22 x2

    Hence the given equation is an homogeneous equation.

    Let  y = v x 

    and  dydx = v + x dvdxSo,    v + x dvdx = 2 x ( v x ) - ( v x )22 x2                          =  2 v - v2 2 = v - v22     x dvdx = - v22     2  1v2 dv = -  dxx     2 - 1v  = - log  x  + C    2 xy =  log  x  + C

    Question 610
    CBSEENMA12035979

    How many times must a man toss a fair coin, so that the probability of having at least one head is more than 80%?

    Solution

    Let the man toss the coin times. then n tosses are n Bernoulli trials

    Probability ( P ) of getting a head at the toss of a coin is  12

     p = 12    q = 12 P ( X - x ) = nCx pn - x qx =  nCx   12 n - x  12 x                        =  nCx   12 n

    It is given that

    P ( getting at least one head ) > 80100

     p ( X  1 ) > 0 . 8 1 - P ( X = 0 )  > 0 . 81 -  nC0 12n < 0 . 8 nC0 12n < 0 . 212n < 0 . 2 2n > 10 . 2 = 5  2n  > 5               ...........( i )

    The minimum value of  n  which satisfies given inequality is  3.

    Thus, the man should toss the coin  3  or more than  3  times.

    Question 611
    CBSEENMA12035987

    Evaluate:  sin x sin 2x sin 3x dx

    Solution

    It is known that,  sin A sin B = 12 cos A - B - cos A + B

      sin x  sin 2 x  sin 3 x   dx =   sin x × 12 cos 2 x - 3 x - cos 2 x + 3 x 

                                            = 12  sin x cos ( - x ) - sin x cos 5 x  dx= 12  sin x cos x - sin x cos 5 x  dx= 12  sin 2 x2  dx -  12  sin x cos 5 x  dx= 14   - cos 2 x 2  - 12  12 sin x + 5 x + sin x - 5 x  dx=  - cos 2 x8  - 14   sin 6 x + sin ( - 4 x )   dx

                                            =  - cos 2 x8  - 14  - cos 6 x6 + cos 4 x4  + C=  - cos 2 x8  - 18  - cos 6 x3 + cos 4 x2  + C=  - cos 2 x8  - 18  2 × (- cos 6 x ) + 3 × cos 4 x 3 × 2   + C=  - cos 2 x8  - 18  - 2 cos 6 x  + 3 cos 4 x 6   + C= 6 × ( - cos 2 x )6 × 8  - 18 × 6   - 2 cos 6 x  + 3 cos 4 x  + C=  - 6 cos 2 x48  - 148  - 2 cos 6 x ) + 3 cos 4 x  + C

                                            = 148  - 6 cos 2 x - ( - 2 cos 6 x  + 3 cos 4 x )  + C= 148  2  cos 6 x  - 3 cos 4 x -  6 cos 2 x )  + C

    Question 612
    CBSEENMA12035988

    Evaluate:  2( 1 - x )   ( 1 + x2 )  dx

    Solution

    Let   2 1 - x   1 + x2  = A1 - x + B x + C1 + x22 = A  1 + x2  +( B x + C )  1 - x 2 = A + A x2 + B x - B x2 + C - C x

    Equating the coefficients of  x2,  x  and  constant term,  we obtain

    A  -  B = 0

    B  -  C = 0

    A  + C = 2

    On solving these equations,  we obtain

    A = 1,  B = 1,   and   C = 1

     2( 1 - x )  ( 1 + x2 ) = 11 - x + x + 11 + x2   2( 1 - x )  ( 1 + x2 )   dx  =  11 - x  dx  +     x1 + x2  dx +   11 + x2  dx= -  1x - 1  dx + 12    2 x1 + x2  dx +   11 + x2  dx= - log  x - 1  + 12 log  1 + x2  + tan- 1 x + C

    Question 613
    CBSEENMA12035991

    Find the equation of the line passing through the point  (-1,3,-2)  and

    perpendicular to the lines   x1 = y2 = z3   and   x + 2- 3 = y - 12 = z + 15.

    Solution

    We know that, equation of a line passing through  x1,  y1,  z1  with direction ratios  a,  b,  c

    Is given by  x - x1a = y - y1b = z - z1c

    So, the required equation of a line passing through ( - 1,  3,  - 2 ) is:

    x + 1a = y - 3b = z + 2c        ..............( i )Given that the line  x1 = y2 = z3  is perpendicular to line ( i ),  soa1 a2 + b1 b2  + c1 c2  = 0a x 1 + b x 2 + c x 3 = 0a + 2 b + 3 c = 0                        .............( ii )And line    x + 2- 3 = y - 12 = z + 15 is perpendicular to line  ( i ),  soa1 a2 + b1 b2  + c1 c2  = 0a x ( - 3 ) + b x 2 + c x 5 = 0- 3 a + 2 b + 5 c = 0                  ............( iii ) 

     

    Solving equation  ( ii )  and  ( iii )  by cross multiplication,

    a2 x 5 - 2 x 3 = b( - 3 ) x 3 - 1 x 5 = c1 x 2 - ( - 3 ) x 2 a10 - 6 = b- 9 - 5 = c2 + 6 a4 = b- 14 = c8 a2 = b- 7 = c4 = λ     ( say ) a = 2 λ,   b = - 7 λ,   c = 4 λ

    Putting the value of  a,  b  and  c  in  ( i ) gives

    x + 12 λ  = y - 3- 7 λ  = z + 24 λ x + 12  = y - 3- 7  = z + 24 

    Question 614
    CBSEENMA12035992

    Find the particular solution of the following differential equation:

    x + 1 dydx = 2 e- y - 1;      y = 0  when  x = 0.

    Solution

     x + 1  dydx = 2 e- y - 1 dy 2 e- y - 1 = dx x + 1 ey 2 - e y = dx x + 1

    Integrating both sides,  we get:

     ey dy2 - ey = log  x + 1  + log C            ............( i )Let   2 - ey = t. ddy =  2 - ey  = dtdy  - ey = dtdy  ey dy = - dt

    substituting this value in equation  ( i ), we get:

     - dtt = log  x + 1  + log C - log   t  =  log  C ( x + 1 )  - log   2 - ey  =  log  C ( x + 1 )  1 2 - ey = C ( x + 1 ) 2 - ey = 1 C ( x + 1 )                     ..............( ii )

    Now,  at  x = 0  and  y = 0,  equation  ( ii ) becomes:

     2 - ey = 1x + 1 ey = 2 - 1x + 1 ey = 2 x + 2 - 1x + 1 ey = 2 x + 1x + 1 y = log   2 x + 1x + 1 ;    x  - 1 

    This is the required particular solution of the given differential equation.

    Question 615
    CBSEENMA12035995

    A manufacturer produces nuts and bolts. It takes 1 hours of work on machine A and 3 hours on machine B to product a package of nuts. It takes 3 hours on machine A and 1 hour on machine B to produce a package of bolts. He earns a profit of `17.50 per package on nuts and `7 per package of bolts. How many packages of each should be produced each day so as to maximize his profits if he operates his machines for at the most 12 hours a day? From the above as a linear programming problem and solve it graphically.

    Solution

    Let the manufacturer produce  x  packages of nuts and  y  packages of bolts.

    Therefore,  x  0    and    y  0.

    The given information can be complied in a table as follows.

     

      Nuts Bolts Availability
    Machine  A ( h ) 1 3 12
    Machine  B ( h ) 3 1 12

     

    The profit on a package o nuts is Rs. 17.50  and  on a package of bolts is Rs. 7.

    Therefore, the constraints are

    x + 3 y  123 x + y   12

    Total profit,  Z = 17.5 x + 7 y

    The mathematical formulation of the given problem is 

    Maximise  Z = 17.5 x + 7 y              ..............( i )

    Subject to the constrain,

    x + 3 y  12                                             ..............( ii )3 x + y  12                                             ..............( iii )x,  y   0                                                   ..............( iv )

    The feasible region determined by the system of constraints is as follows:

                      

    The corner points are  A ( 4, 0 ),  B ( 3, 3 )  and  C ( 0, 4 ).

    The values of  Z  at these corner points are as follows:

     

    corner point Z = 17.5 x + 7 y  
    O ( 0, 0 ) 0  
    A ( 4, 0 ) 70  
    B ( 3, 3 ) 73.5   Maximum
    C ( 0, 4 ) 28  

     

    The maximum values of  Z  is Rs. 73.50  at (3, 3 ).

    Thus,  3 packages of nuts and  3  packages of bolts should be produced each day to get the maximum profit of Rs. 73.50.

    Question 616
    CBSEENMA12035996

    Find the equation of the plane determined by the point A( 3, - 1, 2 ), B( 5, 2, 4 ) and C( -1, -1, 6 ) and hence find the distance between the plane and the point P( 6, 5, 9 ).

    Solution

    We know that, equation of a plane passing through  3  points,

      x - x1    y - y1     z - z1 x2 - x1     y2 - y1      z2 - z1x3 - x1    y3 - y1      z3 - z1    =  0    x - 3       y + 1      z - 22         3    2- 4             0    4    =  0  ( x - 3 ) ( 12 - 0 ) - ( y + 1 ) ( 8 + 8 ) + ( z - 2 ) ( 0 + 12 ) = 0 12 x - 36 - 16 y - 16 + 12 z - 24 = 0 12 x - 16 y + 12 z - 76 = 0 3 x - 4 y + 3 z - 19 = 0

    Also, perpendicular distance of  P ( 6, 5, 9 )  to the plane  3 x - 4 y + 3 z - 19 = 0

    =  3 × 6 - 4 × 5 + 3 × 9 - 19  9 + 16 + 9= 634 units

    Question 617
    CBSEENMA12035997

    Prove that  0π4  tan x +  cot x  dx = 2. π2

    Solution

    0π4  tan x +  cot x  dx = 0π4    sin x cos x  +  cos xsin x   dx= 0π4   sin x + cos xsin x cos x    dx=  2 0π4   sin x + cos x2 sin x cos x    dx=  2 0π4   sin x + cos x1 -  sin x - cos x2   dxPut  sin x - cos x =  t   ( cos x + sin x ) dx = dt

     

    If  x = 0,  t = 0 - 1 = - 1

     

    and if  x = π4,   t = 12 - 12 = 0 0π4  tan x +  cot x  dx =  2 - 10 dt 1 - t2                                                  =  2   sin- 1 t -10                                                  =  2   sin- 1 0 - sin- 1   - 1                                                    =   2   0 + π2                                                   =  2 × π2.

    Question 618
    CBSEENMA12035998

    Evaluate  13 2 x2 + 5 x  dx    as a limit of sum.

    Solution

    13 2 x2 + 5 x  dxHere,  a = 1,  b = 3,  f ( x ) = 2 x2 + 5 x n h = b - a = 3 - 1 = 2Now  ab f ( x ) dx  = limh  0 h  f ( a )  +  f (  a + h ) +  f ( a + 2 h ) + .....+ F ( a + ( n - 1 ) h ) 13 2 x2 + 5 x  dx= limh  0 h  f ( 1 )  +  f (  1 + h ) +  f ( 1 + 2 h ) + .....+ F ( 1 + ( n - 1 ) h )

    = limh  0 h   2 ( 1 )2 + 5 ( 1 ) + 2 ( 1 + h )2 + 5 ( 1 + h ) +  2 ( 1 + 2 h )2 + 5 ( 1 + 2 h ) .......                                                                            +  2 ( 1 + ( n - 1  h )2 + 5 ( 1 + ( n - 1 ) h ) )= limh  0 h   7 +  2 h2 9 h + 7  +  8 h2 + 18 h + 7  +..........                 +  2 ( n - 1 2 h2 + 9 ( n - 1 ) h + 7 )= limh  0 h   7 n + 2 h2 ( 12 + 22 + ........+ ( n - 1 )2 ) + 9 h ( 1 + 2 + ........+ ( n - 1 ) = limh  0 h  7 n + 2 h2  n ( n - 1 ) ( 2 n - 1 )6 + 9 h n ( n - 1 )2

    = limh  0 h  7 n h + 2 n h ( n h - h ) ( 2 n h - h )6 + 9 n h ( n h - h )2 = limh  0 h  14 + 2 2 ( 2 - h ) ( 4 - h )6 + 9 2 ( 2 - h )2 = 14 + 163 + 18=  1123

    Question 619
    CBSEENMA12036000

    A girl throws a die. If she get a 5 OR 6, she tosses a coin three times and notes the number of heads. If she gets 1, 2, 3 OR 4, she tosses a coin two times and notes the number of heads obtained. If she obtained exactly two heads, what is the probability that she threw 1, 2, 3 OR 4 with the die?

    Solution

    Consider the following events:

    E1 = Getting  5  OR  6  in a single throw of the die

    E2 =  Getting  1,  2,  3  OR  4  in a single throw of the die

    A = Getting exactly  2  heads

    We have to find,  P ( E2 | A ).

    Since  P ( E2 | A ) =  P ( A | E2 )  P ( E2 )P ( A | E1 )  P ( E1 )  + P ( A | E2 )  P ( E2 ) Now,  P ( E1 ) =  26 = 13   and    P ( E2 ) = 46 = 23Also,P ( A | E1 ) = Probability  of getting exactly  2  heads when a coin is  tossed  3  times = 38And,  P ( A | E2 ) = Probability  of getting   2  heads when a coin is  tossed  2  times = 12

     P ( E2 | A ) = 12 × 2338 × 13 + 12 × 23                           =  1313  38 + 1   = 1313  38 + 1 × 81 × 8                           = 1313  8 + 38  = 1313  118                           = 1  118   = 811

    Question 620
    CBSEENMA12036001

    Using the method of method of integration, find the area of the region bounded by the following lines:

    3x – y – 3 = 0,

    2x + y – 12 = 0,

    x – 2y – 1 = 0

    Solution

    Given equations are:

    3 x - y = 3         ........( i )                             

    2 x + y = 12      ........( ii )                                     

    x - 2 y = 1         .......( iii )

     

    To solve  ( i )  and  ( ii ),

    ( i ) + ( ii )   5 x = 15    x = 3

    ( ii )   y = 12 - 6 = 6

    Thus  ( i )  and  ( ii )  intersect at  C ( 3, 6 ).

     

    To solve  ( ii )  and  ( iii ),

    ( ii )  - 2 ( iii )   5 y = 10   y = 2

    ( ii )    2 x = 12 - 2 = 10      x = 5

    Thus,  ( ii )  and  ( iii )  intersect at  B ( 5, 2 ).

     

    To solve ( iii )  and  ( i ),

    2 ( i ) - ( iii )    5 x = 5      x = 1

    ( iii )    1 - 2 y = 1      y = 0

    Thus  ( iii )  and  ( i )  intersect at  A ( 1, 0 ).

           

    Area = 13 ( 3 x - 3 )  dx  +  35 ( 12 - 2 x )  dx  - 15 12 ( x - 1 )  dx         = 3  x22 - x 13  +   12 x - x2 35  -  12 x22 - x  15         =  3   92 -3   -   12 - 1   +  ( 60 - 25 ) -  36 - 9   - 12  252 - 5  -  12 - 1  

     

           =  3  32 + 12  +  35 - 27  - 12  152 + 12 = 3  32 + 1 2  +  35 - 27  - 12  152 + 1 2  = 3  42   +  35 - 27  - 12  162  = 3  2   +  35 - 27  - 12  8 

            = 6 + 8 - 4

            = 10 sq. unit

    Question 621
    CBSEENMA12036020

    If one of the diameters of the circle, given by the equation, x2+y2−4x+6y−12=0, is a chord of a circle S, whose centre is at (−3, 2), then the radius of S is:

    • 5 square root of 2
    • 5 square root of 3
    • 5

    • 10

    Solution

    B.

    5 square root of 3

    Given equation of a circle is x2 + y2 -4x +6y -12 = 0, whose centre is (2,-3) and radius
    space equals space square root of 2 squared plus left parenthesis negative 3 right parenthesis squared plus 12 end root
equals square root of 4 plus 9 plus 12 space equals space 5 end root
    Now, according to given information, we have the following figure.

    x2+y2-4x +6y-12 =0
    Clearly, AO perpendicular to BC, as O is mid-point of the chord.
    Now in ΔAOB,. we have
    OA space equals space square root of left parenthesis negative 3 minus 2 right parenthesis squared plus left parenthesis 2 plus 3 right parenthesis squared end root
equals space square root of 25 plus 25 end root space equals space square root of 50 space end root space equals space 5 square root of 2
and space OB space equals space 5
therefore comma
OB space equals space 5
AB space equals space square root of OA squared plus OB squared end root space equals space square root of 50 plus 25 end root space equals space square root of 75 space equals space 5 square root of 3

    Question 623
    CBSEENMA12036022

    The eccentricity of the hyperbola whose length of the latus rectum is equal to 8 and the length of its conjugate axis is equal to half of the distance between its foci, is:

    • 4/3

    • fraction numerator 4 over denominator square root of 3 end fraction
    • fraction numerator 2 over denominator square root of 3 end fraction
    • square root of 3

    Solution

    C.

    fraction numerator 2 over denominator square root of 3 end fraction

    We have, 2b2/a = 8 and 2b = ae
    ⇒ b2 = 4a and 2b = ae
    Consider, 2b = ae
    Consider, 2b = ae
    ⇒ 4b2 = a2e2
    ⇒ 4a2 (e2-1)=a2e2
    ⇒ 4e2-4 = e23 straight e squared space equals space 4 space rightwards double arrow space straight e space equals space fraction numerator 2 over denominator square root of 3 end fraction [e>0]

    Question 625
    CBSEENMA12036026

    If the standard deviation of the numbers 2, 3, a and 11 is 3.5, then which of the following is true?

    • 3a2−26a+55=0

    • 3a2−32a+84=0

    • 3a2−34a+91=0

    • 3a2−23a+44=0

    Solution

    B.

    3a2−32a+84=0

    We know that, if x1, x2..... xn are n observations, then their standard deviation is given by

    square root of 1 over straight n sum straight x subscript straight i superscript 2 space minus open parentheses fraction numerator space stack sum straight x subscript straight i with space below over denominator straight n end fraction close parentheses squared end root
    we begin inline style space end style begin inline style have end style begin inline style comma end style begin inline style space end style begin inline style space end style begin inline style left parenthesis end style begin inline style 3 end style begin inline style. end style begin inline style 5 end style begin inline style right parenthesis squared end style begin inline style space end style begin inline style equals end style begin inline style space end style fraction numerator left parenthesis 2 squared space plus 3 squared space plus straight a squared plus 11 squared right parenthesis over denominator 4 end fraction begin inline style space end style begin inline style minus end style begin inline style space end style begin inline style open parentheses begin display style fraction numerator 2 plus 3 plus straight a plus 11 over denominator 4 end fraction end style close parentheses squared end style begin inline style space end style begin inline style space end style begin inline style space end style
    space begin inline style rightwards double arrow end style begin inline style space end style 49 over 9 begin inline style space end style begin inline style equals end style begin inline style space end style fraction numerator 4 space plus space 9 space plus straight a squared plus 121 over denominator 4 end fraction begin inline style minus end style begin inline style open parentheses begin display style fraction numerator 16 plus straight a over denominator 4 end fraction end style close parentheses squared end style begin inline style space end style begin inline style space end style begin inline style space end style begin inline style space end style begin inline style space end style
begin inline style rightwards double arrow end style begin inline style space end style 49 over 9 begin inline style space end style begin inline style equals end style begin inline style space end style fraction numerator 134 space plus straight a squared over denominator 4 end fraction begin inline style minus end style fraction numerator 256 space plus straight a squared plus 32 straight a over denominator 16 end fraction begin inline style space end style begin inline style space end style begin inline style space end style begin inline style space end style begin inline style space end style
    49 over 9 begin inline style space end style begin inline style equals end style begin inline style space end style fraction numerator 4 straight a squared space plus 536 minus 256 minus straight a squared minus 32 straight a over denominator 16 end fraction
    space begin inline style space end style begin inline style 49 end style begin inline style space end style begin inline style straight x end style begin inline style space end style begin inline style 4 end style begin inline style space end style begin inline style equals end style begin inline style space end style begin inline style 3 end style begin inline style straight a squared end style begin inline style minus end style begin inline style 32 end style begin inline style straight a end style begin inline style plus end style begin inline style 280 end style begin inline style space end style begin inline style 3 end style begin inline style straight a squared end style begin inline style minus end style begin inline style 32 end style begin inline style straight a end style begin inline style space end style begin inline style plus end style begin inline style space end style begin inline style 84 end style begin inline style space end style begin inline style equals end style begin inline style 0 end style

    Question 626
    CBSEENMA12036029

    The Boolean Expression (p∧~q)∨q∨(~p∧q) is equivalent to:

    • ~p ∧ q

    • p ∧ q

    • p ∨ q

    • p ∨ ~ q

    Solution

    C.

    p ∨ q

    Consider, (p ∧~q) ∨ q ∨(~p ∧ q)
    ≡ [(p ∧~q) ∨ q] ∨ (~p ∧ q)
    ≡[(p ∨~q) ∧ t] ∨ (~p ∧ q)
    ≡((p ∨ q) ∨ (~p ∧ q)
    ≡(p ∨ q ∨ ~p) ∧ (p ∨ q ∨ q)
    ≡(q ∨ t) ∧ (p ∨ q)
    ≡ t ∧ (p ∨ q)
    ≡ p ∨ q

    Question 627
    CBSEENMA12036038

    The area (in sq units) of the region described by {x,y): y2 ≤ 2x and y ≥ 4x-1} is

    • 7/32

    • 5/64

    • 15/64

    • 9/32

    Solution

    D.

    9/32

    Given region is {x,y): y2 ≤ 2x and y ≥ 4x-1} y2 ≤ 2x  represents a region inside the parabola,
     y2 = 2x   .. (i)
    and y ≥ 4x-1 represents a region to the left of the line
     y = 4x-1 .... (ii)
    The point of intersection of the curve (i) and (ii) is 
    (4x-1)2  = 2x
    ⇒ 16x2 + 1-8x = 2x
    16x2-10x+1 = 0
     x = 1/2, 1/8
    therefore, the points where these curves intersects, are 
    open parentheses 1 half comma 1 close parentheses space space and space open parentheses 1 over 8 comma negative 1 half close parentheses
    Hence, required area,
    integral subscript negative 1 divided by 2 end subscript superscript 1 open parentheses fraction numerator straight y plus 1 over denominator 4 end fraction minus straight y squared over 2 close parentheses space dy
space equals space 1 fourth open parentheses straight y squared over 2 plus straight y close parentheses subscript negative 1 divided by 2 end subscript superscript 1 space minus space 1 over 6 left parenthesis straight y cubed right parenthesis to the power of 1 subscript negative 1 divided by 2 end subscript
equals space 1 fourth open curly brackets open parentheses 1 half plus 1 close parentheses minus open parentheses 1 over 8 minus 1 half close parentheses close curly brackets minus 1 over 6 open curly brackets 1 plus 1 over 8 close curly brackets
space equals space 1 fourth space open curly brackets 3 over 2 space plus 3 over 8 close curly brackets minus 1 over 6 open curly brackets 9 over 8 close curly brackets
space equals space 1 fourth space straight x space 15 over 8 space minus space 3 over 16 space equals space 9 over 32

    Question 628
    CBSEENMA12036039

    Let y(x) be the solution of the differential equation left parenthesis straight x space log space straight x right parenthesis dy over dx space plus straight y space equals space 2 space straight x space log space straight x comma (x  ≥1). Then, y (e) is equal to 

    • e

    • 0

    • 2

    • 2e

    Solution

    C.

    2

    Given differential equation is 
    straight x left parenthesis log space straight x right parenthesis dy over dx space plus straight y space equals 2 space straight x space log space straight x comma
rightwards double arrow space dy over dx space plus fraction numerator straight y over denominator straight x space log space straight x end fraction space equals 2
    This is a linear differential equation.
    therefore,IF space equals space straight e to the power of integral fraction numerator 1 over denominator straight x space log space straight x end fraction dx end exponent space equals space straight e to the power of log space left parenthesis log space straight x right parenthesis space end exponent space equals space log space straight x
    Now, the solution of given differential equation is given by
    straight y. space log space straight x space equals space integral log space straight x. space 2 dx
straight y. space log space straight x space equals space space equals space 2 integral log space straight x space dx
At space straight y. space log space straight x space equals space 2 left square bracket space straight x space log space straight x minus straight x right square bracket plus straight c
straight x space equals space 1
straight c space equals 2
straight y. space log space straight x space equals space 2 left square bracket straight x space log space straight x minus straight x right square bracket plus 2
straight x space equals straight e
straight y space equals space 2 space left parenthesis straight e minus straight e right parenthesis space plus 2 space rightwards double arrow straight y space equals space 2

    Question 629
    CBSEENMA12036042

    The area (in sq units) of the quadrilateral formed by the tangents at the end points of the latera recta to the ellipsestraight x squared over 9 plus straight y squared over 5 space equals space 1 space is space

    • 27/4

    • 18

    • 27/2

    • 27

    Solution

    D.

    27

    given equation of ellipse is 
    straight x squared over 9 space plus space straight y squared over 5 space equals space 1
straight a squared space equals space 9 comma space straight b squared space equals 5
straight a space equals 3 comma space straight b space equals space square root of 5
straight e space equals square root of 1 minus straight b squared over straight a squared end root space equals space square root of 1 minus 5 over 9 end root space equals space 2 over 3
foci space left parenthesis space plus-or-minus space ae comma space 0 right parenthesis space space equals left parenthesis plus-or-minus 2 comma 0 right parenthesis
and space straight b squared over straight a space equals space 5 over 3
    Therefore, Extremities of one of latus rectum are
    open parentheses 2 comma 5 over 3 close parentheses space and space open parentheses 2 comma fraction numerator negative 5 over denominator 3 end fraction close parentheses space
Therefore comma space Equation space of space tangent space at space open parentheses 2 comma 5 over 3 close parentheses space is comma
fraction numerator straight x left parenthesis 2 right parenthesis over denominator 9 end fraction space plus fraction numerator straight y left parenthesis 5 divided by 3 right parenthesis over denominator 5 end fraction space equals space 1
or space 2 straight x space plus space 3 straight y space equals space 9
Eq. space left parenthesis ii right parenthesis space intersects space straight X space and space straight Y space minus axes space at space open parentheses 0 comma 9 over 2 close parentheses space and space left parenthesis 0 comma 3 right parenthesis
    therefore, area of quadrilateral = 4 x Area of ΔPOQ
     = 4 space straight x space open parentheses 1 half straight x 9 over 2 straight x 3 close parentheses
    = 27 sq units

    Question 630
    CBSEENMA12036043

    Let O be the vertex and Q be nay point on the parabola x2 = 8y. If the point P divides the line segment OQ internally in the ratio 1:3 then the locus of P is 

    • x2= y

    • y2 =x

    • y2 =2x

    • x2 = 2y

    Solution

    D.

    x2 = 2y

    Any point on the parabola x2 = 8y is (4t, 2t2). Point P divides the line segment joining of O (0,0) and Q (4t,2t2) in the ratio 1:3 Apply the section formula for the internal division.
    the equation of the parabola is
    x2 = 8y
    Let any Q on the parabola (i) is (4t, 2t2).
    Let P (h,k) be the point which divides the line segment joining (0,0) and (4t, 2t2) in the ratio 1:3.

    straight h space equals space fraction numerator 1 space straight x space 4 straight t plus 3 straight x 0 over denominator 4 end fraction
straight h space equals straight t
straight k space equals space fraction numerator 1 space straight x space 2 straight t squared straight x 3 space straight x 0 over denominator 4 end fraction space rightwards double arrow space straight k space equals space straight t squared divided by 2
rightwards double arrow space straight k space equals space 1 half straight h squared
2 straight k space equals space straight h squared space rightwards double arrow space 2 straight y space equals space straight x squared

    Question 632
    CBSEENMA12036051

    If =-1 and x =2 are extreme points of f(x) =α log|x| + βx2 +x, then

    • α = -6, β = 1/2

    • α = -6, β = -1/2

    • α = 2, β = -1/2

    • α = 2, β = 1/2

    Solution

    C.

    α = 2, β = -1/2

    Here, x =-1 and x = 2 are extreme points of f(x) = α log|x| +βx2 +x then,
    f'(x) = α/x +2βx + 1
    f'(-1) = -α -2β +1 = 0  .... (i)
    [At extreme point f'(x) = 0]
    f'(2) = α/x +4βx + 1 = 0 .. (ii)
    On solving Eqs (i) and (ii), we get
    α = 2 and β = -1/2

    Question 633
    CBSEENMA12036054

    The area of the region described by A = {(x,y): x2 +y2 ≤ 1 and y2 ≤1-x} is

    • straight pi over 2 plus 4 over 3
    • straight pi over 2 minus 2 over 3
    • straight pi over 2 minus 2 over 3
    • straight pi over 2 space plus 2 over 3

    Solution

    A.

    straight pi over 2 plus 4 over 3

    Given, {(x,y): x2 +y2 ≤ 1 and y2 ≤1-x}
    Required area = 1 half πr squared space plus space 2 space integral subscript 0 superscript 1 left parenthesis 1 minus straight y squared right parenthesis dy
equals space 1 half straight pi left parenthesis 1 right parenthesis squared space plus space 2 space open parentheses straight y minus straight y cubed over 3 close parentheses subscript 0 superscript 1
equals space straight pi over 2 plus 4 over 3

    Question 634
    CBSEENMA12036055

    Let the population of rabbits surviving at a time t be governed by the differential equation.fraction numerator dp left parenthesis straight t right parenthesis over denominator dt end fraction space equals space 1 half straight p left parenthesis straight t right parenthesis space minus 200 If p(0) = 100 then p(t) is equal to 

    • 400 minus 300 straight e to the power of straight t over 2 end exponent
    • 300 minus 200 straight e to the power of negative straight t over 2 end exponent
    • 600 minus 500 straight e to the power of straight t over 2 end exponent
    • 400 minus 300 straight e to the power of negative straight t over 2 end exponent

    Solution

    A.

    400 minus 300 straight e to the power of straight t over 2 end exponent

    Given differential equation dp over dt minus 1 half straight p left parenthesis straight t right parenthesis space equals space minus 200 is a linear differential equation
    Here, p(t) = fraction numerator negative 1 over denominator 2 end fraction comma space straight Q space left parenthesis straight t right parenthesis space equals space minus space 200
     If space equals space straight e to the power of integral negative open parentheses 1 half close parentheses dt end exponent space equals space straight e to the power of negative 1 half end exponent
    Hence, solution is 
    p(t), IF = ∫Q(t)IF dt
    straight p left parenthesis straight t right parenthesis. straight e to the power of negative straight t over 2 end exponent space equals space integral negative 200. straight e to the power of negative straight t over 2 end exponent dt
straight p left parenthesis straight t right parenthesis. straight e to the power of negative straight t over 2 end exponent space equals integral negative 200 space straight e to the power of negative straight t over 2 end exponent. dt
straight p left parenthesis straight t right parenthesis. straight e to the power of negative straight t over 2 end exponent space equals space 400 space straight e to the power of negative straight t over 2 end exponent space plus space straight K
rightwards double arrow space straight p left parenthesis straight t right parenthesis space equals space 400 space plus ke to the power of negative 1 half end exponent
If space straight p left parenthesis 0 right parenthesis space equals space 100 space comma then space straight k space equals negative 300
rightwards double arrow space straight p left parenthesis straight t 0 space equals space 400 space minus 300 to the power of straight t over 2 end exponent

    Question 637
    CBSEENMA12036066

    The intercepts on X- axis made by tangents to the curve, straight y space equals space integral subscript 0 superscript straight x vertical line straight t vertical line space dt comma space straight x space straight epsilon space straight R which are parallel to the line y =2x, are equal to

    • ±1

    • ±2

    • ±3

    • ±4

    Solution

    A.

    ±1

    integral subscript 0 superscript straight x space vertical line straight t vertical line space dt comma space parallel space to space straight y space equals space 2 straight x
therefore space dy over dx space equals space vertical line straight x vertical line space equals space 2
straight x space equals space plus-or-minus 2
therefore space Points comma space straight y space equals space integral subscript 0 superscript plus-or-minus 2 end superscript vertical line straight t vertical line space dt space equals space plus-or-minus 2
    ∴ Equation of tangent is
    y-2 = 2(x-2)
    and y +2 = 2 (x+2)
    for x - intercept, put y = 0, we get
     0- 2 = 2(x-2)
    and 0+2 = 2(x+2)
    x = ±1
    Question 638
    CBSEENMA12036068

    Let straight a with hat on top space and space straight b with hat on top be  two unit vectors. If the vectors straight c equals space straight a with hat on top space plus 2 straight b with hat on top and straight d space equals space 5 straight a with hat on top space minus 4 straight b with hat on top are perpendicular to each other, then the angle between straight a with hat on top space and space straight b with hat on top is 

    • π/6

    • π/2

    • π/3

    • π/4

    Solution

    C.

    π/3

    straight a with hat on top space and space straight b with hat on top space are space unit space vecotr comma space straight i. straight e comma space vertical line straight a with hat on top vertical line space equals space vertical line straight b with hat on top vertical line space equals 11
ii right parenthesis space straight C space equals straight a with hat on top space plus 2 straight b with hat on top space and space straight d space equals space 5 straight a with hat on top space minus 4 straight b with hat on top
    (iii) c and d are perpendicular to each other, i.e., c.d =0
    To find Angle between a and b
    Now, c.d = 0
    left parenthesis straight a with hat on top space plus 2 straight b with hat on top right parenthesis. left parenthesis 5 straight a with hat on top space minus 4 straight b with hat on top right parenthesis space equals space 0
rightwards double arrow space 5 straight a with hat on top. straight a with hat on top space minus space 4 space straight a with hat on top. straight b with hat on top space plus space 10 straight b with hat on top. straight a with hat on top space minus 8 space straight b with hat on top. straight b with hat on top space equals space 0
rightwards double arrow space 6 straight a with hat on top. straight b with hat on top space equals 3
rightwards double arrow space straight a with hat on top. straight b with hat on top space equals space 1 half
rightwards double arrow space vertical line stack straight a vertical line with hat on top vertical line straight b with hat on top vertical line space cos space straight theta space equals space cos space straight pi over 3
rightwards double arrow space Angle space between space straight a with hat on top space and space straight a with hat on top space is straight pi over 3
    Question 641
    CBSEENMA12036083
    Question 643
    CBSEENMA12036092

    If space straight a with rightwards arrow on top space equals space fraction numerator 1 over denominator square root of 10 end fraction space left parenthesis 3 straight i with hat on top space plus straight k with hat on top right parenthesis space and space straight b with rightwards arrow on top space equals space 1 over 7 left parenthesis 2 straight i with hat on top space plus space 3 straight j with hat on top space minus 6 straight k with hat on top right parenthesis comma space then space the space value space of space left parenthesis 2 straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis. left square bracket left parenthesis straight a with rightwards arrow on top space straight x space straight b with rightwards arrow on top right parenthesis space straight x left parenthesis straight a with rightwards arrow on top plus 2 straight b with rightwards arrow on top right parenthesis right square bracket space is
    • -5

    • -3

    • 5

    • 3

    Solution

    A.

    -5

    left parenthesis 2 straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis. left square bracket left parenthesis straight a with rightwards arrow on top space straight x straight b with rightwards arrow on top right parenthesis space straight x space left parenthesis straight a with rightwards arrow on top space plus 2 straight b with rightwards arrow on top right parenthesis right square bracket
equals negative space left parenthesis 2 straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis. left square bracket space left parenthesis straight a with rightwards arrow on top space plus 2 straight b with rightwards arrow on top right parenthesis straight x space left parenthesis straight a with rightwards arrow on top space straight x straight b with rightwards arrow on top right parenthesis space right square bracket
equals space minus space left parenthesis 2 straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis. left square bracket left parenthesis straight a with rightwards arrow on top plus 2 straight b with rightwards arrow on top right parenthesis. straight b with rightwards arrow on top right parenthesis straight a with rightwards arrow on top minus left parenthesis straight a with rightwards arrow on top plus 2 straight b with rightwards arrow on top right parenthesis. straight a with rightwards arrow on top right parenthesis straight b with rightwards arrow on top right square bracket
space equals space minus space left parenthesis 2 straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis. left square bracket left parenthesis straight a with rightwards arrow on top. straight b with rightwards arrow on top right parenthesis plus 2. straight b with rightwards arrow on top. straight b with rightwards arrow on top right parenthesis straight a with rightwards arrow on top minus left parenthesis straight a with rightwards arrow on top. straight a with rightwards arrow on top plus 2 straight b with rightwards arrow on top. straight a with rightwards arrow on top right parenthesis straight b with rightwards arrow on top right parenthesis right square bracket
equals space minus space left parenthesis 2 straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis. left square bracket 0 space plus 2 straight a with rightwards arrow on top minus left parenthesis 0 space plus straight b with rightwards arrow on top right parenthesis right square bracket
equals negative left parenthesis 2 straight a with rightwards arrow on top space minus straight b with rightwards arrow on top right parenthesis. space left parenthesis 2 straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis
equals negative space left parenthesis 2 straight a with rightwards arrow on top minus straight b with rightwards arrow on top right parenthesis squared space equals space minus 4 straight a with rightwards arrow on top squared space plus 4 straight a with rightwards arrow on top. straight b with rightwards arrow on top minus straight b with rightwards arrow on top squared
space equals space minus space 4 plus 0 minus 1 space equals space minus space 5
    Question 646
    CBSEENMA12036110

    Solution of the differential equation
    cos x dy = y (sin x - y) dx, 0 < x < π/2, is 

    • sec x = (tan x + C ) y 

    •  y sec x = tan x + C

    •  y tan x = sec x + C 

    •  tan x = (sec x  + C)y

    Solution

    A.

    sec x = (tan x + C ) y 

    since cos xdy = y sin x dx - ydx
    rightwards double arrow space 1 over straight y squared space dy over dx minus 1 over straight y space tan space straight x space equals space minus space sec space straight x
Put space minus 1 over straight y space equals space straight z
rightwards double arrow 1 over straight y squared dy over dx space equals space dz over dx
rightwards double arrow space dz over dx space plus space left parenthesis tan space straight x right parenthesis straight z space equals space minus space sec space straight x
    This is linear differential equation,
    Therefore,
    IF space equals space straight e to the power of integral tan space straight x space dx end exponent equals space straight e to the power of log space sec space straight x space end exponent space equals space sec space straight x
Hence comma space the space solution space is
straight z. space left parenthesis sec space straight x right parenthesis space equals space integral negative sec space straight x. space sec space straight x space dx space plus space straight C subscript 1
rightwards double arrow space minus 1 over straight y space sec space straight x space equals space minus space tan space straight x space plus space straight C subscript 1
rightwards double arrow space sec space straight x space equals space straight y space left parenthesis space tan space straight x space plus space straight C right parenthesis

    Question 647
    CBSEENMA12036113
    Question 648
    CBSEENMA12036115

    Let bold a bold space bold equals bold j with bold hat on top bold minus bold k with bold hat on top bold space and bold c bold space bold equals bold space bold i with bold hat on top bold minus bold j with bold hat on top bold minus bold k with bold hat on top. Then, the vector b satisfying a x b + c = 0  and a.b  = 3

    • negative straight i with hat on top plus straight j with hat on top space minus 2 straight k with hat on top
    • 2 straight i with hat on top minus straight j with hat on top space plus 2 straight k with hat on top
    • negative straight i with hat on top minus straight j with hat on top space minus 2 straight k with hat on top
    • straight i with hat on top plus straight j with hat on top space minus 2 straight k with hat on top

    Solution

    A.

    negative straight i with hat on top plus straight j with hat on top space minus 2 straight k with hat on top

    a x b +c = 0
    ⇒ a x (a x b) + a x c = 0
    ⇒ (a.b)a-(a.a)b +a x c = 0
    ⇒ 3a - 2b + a x c = 0
    ⇒ 2b = 3a +a x c
    rightwards double arrow space 2 straight b space equals space 3 straight j with hat on top minus 3 straight k with hat on top space minus 2 straight i with hat on top space minus straight j with hat on top space minus straight k with hat on top
space equals space minus 2 straight i with hat on top space plus space 2 straight j with hat on top space minus 4 straight k with hat on top
rightwards double arrow space straight b space equals negative straight i with hat on top space plus straight j with hat on top minus 2 straight k with hat on top 

    Question 649
    CBSEENMA12036116

    If the vectors bold a bold space bold equals bold space bold i with bold hat on top bold space bold minus bold j with bold hat on top bold space bold plus bold 2 bold k with bold hat on top bold comma bold space bold b bold space bold equals bold 2 bold i with bold hat on top bold space bold plus bold 4 bold j with bold hat on top bold space bold plus bold k with bold hat on top bold space bold and bold space bold c bold space bold equals bold space bold lambda bold i with bold hat on top bold space bold plus bold j with bold hat on top bold space bold plus bold mu bold k with bold hat on top are mutually orthogonal, then (λ,μ) is equal to

    • (-3,2)

    • (2,-3)

    • (-2,3)

    • (3,-2)

    Solution

    A.

    (-3,2)

    since, the given vectors mutually orthogonal, therefore
    a.b = 2-4+2 = 0
    a.c = λ-1 + 2μ = 0   ....(i)
    b.c = 2λ + 4 +μ = 0  ... (ii)
    On solving Eqs. (i) and (ii), we get
    μ  = 2 and λ = - 3
    Hence, (λ,μ) = (-3,2)

    Question 651
    CBSEENMA12036126

    Let space straight a with rightwards arrow on top space equals space 2 straight i with hat on top space plus straight j with hat on top minus 2 straight k with hat on top space and space straight b with rightwards arrow on top space equals straight i with hat on top space plus straight j with hat on top. space Let space straight c with rightwards arrow on top space be space straight a space vector space such space that space vertical line straight c with rightwards arrow on top minus straight a with rightwards arrow on top vertical line equals 3
vertical line left parenthesis straight a with rightwards arrow on top space straight x straight b with rightwards arrow on top right parenthesis space straight x straight c with rightwards arrow on top vertical line space equals space 3 space and space the space angle space between space straight c with rightwards arrow on top space and space straight a with rightwards arrow on top space straight x space straight b with rightwards arrow on top space be space 30 to the power of straight o. space Then space straight a with rightwards arrow on top. straight c with rightwards arrow on top space is space
equal space to space
    • 1/8

    • 25/8

    • 2

    • 5

    Solution

    C.

    2

    straight a with rightwards arrow on top space equals space 2 straight i with hat on top space plus straight j with hat on top minus 2 straight k with hat on top comma
straight b with rightwards arrow on top space equals space straight i with hat on top space plus straight j with hat on top space and space vertical line straight a with hat on top vertical line space equals space 3
therefore comma space straight a with rightwards arrow on top space straight x straight b with rightwards arrow on top space equals space space 2 straight i with hat on top space minus 2 straight j with hat on top plus straight k with hat on top comma
left parenthesis straight a with rightwards arrow on top space straight x straight b with rightwards arrow on top right parenthesis space straight x straight c with rightwards arrow on top space equals space vertical line straight a with rightwards arrow on top space straight x straight b with rightwards arrow on top vertical line vertical line straight c with rightwards arrow on top vertical line space sin space 30 space straight n with hat on top
vertical line left parenthesis straight a with rightwards arrow on top space straight x space straight b with rightwards arrow on top right parenthesis space straight x space straight c with rightwards arrow on top vertical line space equals space 3. vertical line straight c with rightwards arrow on top vertical line.1 half
3 space equals space 3 vertical line straight c with rightwards arrow on top vertical line.1 half
therefore space vertical line straight c with rightwards arrow on top vertical line space equals space 2
Now colon space vertical line straight c with rightwards arrow on top minus straight a with rightwards arrow on top vertical line space equals space 3
straight c squared space plus straight a squared space minus 2 straight c with rightwards arrow on top. straight a with rightwards arrow on top space equals space 9
4 space plus space 9 space minus 2 straight a with rightwards arrow on top. straight c with rightwards arrow on top space equals space 9
straight a with rightwards arrow on top. straight c with rightwards arrow on top space equals space 2
    Question 652
    CBSEENMA12036128

    If left parenthesis 2 space sin space straight x right parenthesis space dy over dx space plus space left parenthesis space straight y space plus 1 right parenthesis space cos space straight x space equals space 0 space and space straight y left parenthesis 0 right parenthesis space equals 1 space then space straight y open parentheses straight pi over 2 close parentheses is equal to

    • 4/3

    • 1/3

    • -2/3

    • -4/3

    Solution

    B.

    1/3

    left parenthesis 2 space plus space sin space straight x right parenthesis dy over dx plus left parenthesis straight y space plus 1 right parenthesis space cos space straight x space equals 0
straight d over dx left parenthesis 2 space plus space sin space straight x right parenthesis space left parenthesis straight y plus 1 right parenthesis space equals 0
left parenthesis 2 space plus space sin space straight x right parenthesis space left parenthesis straight y plus 1 right parenthesis space equals space straight c
straight x space equals space 0 comma space straight y space equals 1
rightwards double arrow space straight c space equals 4
straight y space plus 1 space equals space fraction numerator 4 over denominator 2 space plus space sin space straight x end fraction
straight y open parentheses straight pi over 2 close parentheses space equals space 4 over 3 minus 1 space equals space 1 third
    Question 653
    CBSEENMA12036129

    Let In ∫tan x dx,(n> 1) . I4 + I6 = a tan5x + bx5 + C, where C is a constant of integration, then the ordered pair (a, b) is equal to

    • open parentheses negative 1 fifth comma 0 close parentheses
    • open parentheses negative 1 fifth comma 1 close parentheses
    • open parentheses 1 fifth comma 0 close parentheses
    • open parentheses 1 fifth comma negative 1 close parentheses

    Solution

    C.

    open parentheses 1 fifth comma 0 close parentheses

    I4 +I6 = ∫(tan4x + tan6x) dx
    = ∫tan4 x sec2 x dx
    = 1/5 tan5 x + c
    ⇒ a = 1/5, b = 0

    Question 655
    CBSEENMA12036146
    Question 660
    CBSEENMA12036184

    Let space straight a with minus on top space equals space straight i with hat on top space plus straight j with hat on top space plus straight k comma space straight b with bar on top space equals space straight i with hat on top space minus straight j with hat on top space plus 2 straight k with hat on top space and space straight c with bar on top space equals space straight x straight i with hat on top space plus space left parenthesis straight x minus 2 right parenthesis straight j with hat on top minus straight k with hat on top.
If space the space vector space straight c with bar on top space lies space in space the space plane space of space straight a with bar on top space and space straight b with bar on top comma space then space straight x space equals
    • 0

    • -1

    • -2

    • -4

    Solution

    C.

    -2

    straight a with rightwards arrow on top space equals space straight i with hat on top space plus straight j with hat on top space plus straight k with hat on top
straight b with rightwards arrow on top space equals space straight i with hat on top space minus straight j with hat on top space plus 2 straight k with hat on top
straight c with rightwards arrow on top space equals space straight x straight i with hat on top space plus left parenthesis straight x minus 2 right parenthesis straight j with hat on top space minus straight k with hat on top
open vertical bar table row straight x cell straight x minus 2 end cell cell negative 1 end cell row 1 1 1 row 1 cell negative 1 end cell 2 end table close vertical bar space equals 0
3 straight x plus 2 space minus straight x plus 2 space equals 0
2 straight x equals negative 4
straight x equals negative 2
    Question 666
    CBSEENMA12036215
    Question 667
    CBSEENMA12036236

    For any vector straight a with rightwards arrow on top  the value of left parenthesis straight a with rightwards arrow on top space straight x straight i with hat on top right parenthesis squared space plus left parenthesis straight a with rightwards arrow on top space straight x straight j with hat on top right parenthesis squared space plus left parenthesis straight a with rightwards arrow on top space straight x straight k with hat on top right parenthesis squared is equal to

    • 3 straight a with rightwards arrow on top squared
    • straight a with rightwards arrow on top squared
    • 2 straight a with rightwards arrow on top squared
    • 4 straight a with rightwards arrow on top squared

    Solution

    C.

    2 straight a with rightwards arrow on top squared Let space straight a with rightwards arrow on top space equals space straight x straight i with hat on top plus straight y straight j with hat on top plus straight z straight k with hat on top
straight a with rightwards arrow on top space straight x space straight i with hat on top space equals space straight z straight j with hat on top space minus space straight y straight k with hat on top
rightwards double arrow left parenthesis straight a with rightwards arrow on top space straight x space straight i with hat on top right parenthesis squared space equals space straight y squared plus straight z squared
rightwards double arrow left parenthesis straight a with rightwards arrow on top space straight x space straight j with hat on top right parenthesis space equals space straight x squared plus straight z squared
rightwards double arrow left parenthesis straight a with rightwards arrow on top space straight x space straight k with hat on top right parenthesis space equals space straight x squared plus straight y squared
similarly space left parenthesis straight a with rightwards arrow on top space straight x space straight j with hat on top right parenthesis squared space equals space straight x squared plus straight z squared
and space open parentheses straight a with rightwards arrow on top space straight x stack space straight k with hat on top close parentheses squared space equals space straight x squared plus straight y squared
rightwards double arrow space left parenthesis straight a with rightwards arrow on top space straight x space straight i with hat on top right parenthesis squared space plus space left parenthesis straight a with rightwards arrow on top space straight x straight j with hat on top right parenthesis squared space plus space left parenthesis straight a with hat on top space straight x straight k with hat on top right parenthesis squared space equals space 2 space left parenthesis straight x squared space plus straight y squared plus space straight z squared right parenthesis space equals space 2 straight a with rightwards arrow on top squared
    Question 670
    CBSEENMA12036241

    Let space straight a with rightwards arrow on top space equals space straight i with hat on top space minus straight k with hat on top comma space straight b with rightwards arrow on top space equals space straight x straight i with hat on top space plus straight j with hat on top space plus left parenthesis 1 minus straight x right parenthesis space straight k with hat on top space and space
straight c with rightwards arrow on top space equals space straight y straight i with hat on top space plus straight x space straight j with hat on top space plus left parenthesis 1 plus straight x minus straight y right parenthesis straight k with hat on top space. Then space left square bracket straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top right square bracket depends on
    • only y

    • only x

    • both x and y

    • neither x nor y

    Solution

    D.

    neither x nor y

    straight a with rightwards arrow on top space equals space straight i with hat on top minus straight k with hat on top comma space straight b with rightwards arrow on top space equals space straight x straight i with rightwards arrow on top space plus straight j with rightwards arrow on top space plus left parenthesis 1 minus straight x right parenthesis straight k with hat on top space and space straight c with rightwards arrow on top space equals straight y straight i with hat on top space plus straight x straight j with hat on top space plus left parenthesis 1 plus straight x minus straight y right parenthesis straight k with hat on top
left square bracket straight a with rightwards arrow on top straight b with rightwards arrow on top straight c with rightwards arrow on top right square bracket space equals space straight a with rightwards arrow on top. space left parenthesis straight b with rightwards arrow on top straight x straight c with rightwards arrow on top right parenthesis
straight b with rightwards arrow on top space straight x straight c with rightwards arrow on top space equals space open vertical bar table row cell straight i with hat on top end cell cell straight j with hat on top end cell cell straight k with hat on top end cell row straight x 1 cell 1 minus straight x end cell row straight y straight x cell 1 plus straight x minus straight y end cell end table close vertical bar
space equals space straight i with hat on top space left parenthesis 1 plus space straight x minus straight x minus straight x squared right parenthesis minus space straight j with hat on top space left parenthesis straight x plus straight x squared minus xy minus straight y plus xy right parenthesis space plus straight k with hat on top space left parenthesis straight x squared minus straight y right parenthesis
straight a with rightwards arrow on top. left parenthesis straight b with rightwards arrow on top straight x straight c with rightwards arrow on top right parenthesis space equals space 1
    which does not depend on x and y.
    Question 674
    CBSEENMA12036278

    If space straight a with bar on top comma space straight b with bar on top comma straight c with bar on top space are non-coplanar vectors and λ is a real number, then the vectors straight a with bar on top space plus 2 straight b with bar on top space plus 3 straight c with bar on top space comma space straight lambda straight b with bar on top space plus 4 space straight c with bar on top space and space left parenthesis 2 straight lambda space minus 1 right parenthesis straight c with bar on top are non-coplanar for
    • all values of λ

    • all except one value of λ

    • all except two values of λ

    • no value of λ

    Solution

    C.

    all except two values of λ

    Condition for given three vectors to be coplanar is open vertical bar table row 1 2 3 row 0 straight lambda 4 row 0 0 cell 2 straight lambda minus 1 end cell end table close vertical bar =0
     ⇒ λ = 0, 1/2.
    Hence given vectors will be non coplanar for all real values of λ except 0, 1/2.

    Question 677
    CBSEENMA12036288

    Let u be a vector coplanar with the vectors a a = 2i^ + 3j^ -k^ and b = j^ +k^.  if u is perpendicular to a and u.b = 24, then |u| is equal to:

    • 84

    • 336

    • 315

    • 256

    Solution

    B.

    336

    [u.a.b] = 0 u = xa + ybu.a = 0 xa2 + ya.b = 0u.b = 24xab + yb2 = 24(14 x 2y = 0) -(2x +2y = 24)= 12x = - 24x = -2y = 14u = - 2a + 14bu  = -4i^ + 8j^ + 15k^|u| = 42 +82 + 162|u| = 336|u|2 = 336

    Question 678
    CBSEENMA12036302

    The length of the projection of the line segment joining the points (5, –1, 4) and (4, –1, 3) on the plane, x + y + z = 7 is:

    • 23

    • 23

    • 2/3

    • 1/3

    Solution

    A.

    23

    Normal to the plane x + y +z = 7 is

    n = i^ + j^ + k^AB = - i^ - k^  AB = AB = 2BC = Length of projection of AB on n = |AB.n|= (-i^ - k^). ( i^ + j^ + k^)3 = 23Length of projection of the line segment on the plane is ACAC2 = AB2 - BC2 = 2-43 = 23AC2 = 23

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