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Vector Algebra

Question
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 


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