JEE mathematics

Sponsor Area

Question
CBSEENMA11015445

The sum of all real values of x satisfying the equation
left parenthesis straight x squared minus 5 straight x space plus 5 right parenthesis to the power of straight x squared plus 4 straight x minus 60 space equals space 1 end exponent is:

  • 3

  • -4

  • 6

  • 5

Solution

A.

3

Given, 
left parenthesis straight x squared minus 5 straight x space plus 5 right parenthesis to the power of straight x squared plus 4 straight x minus 60 end exponent space equals space 1
clearly comma space this space is space possible space when
straight I. space straight x squared space plus space 4 straight x minus 60 space equals space 0 space and space straight x squared minus 5 straight x space plus 5 space not equal to space 0
II. space straight x squared minus 5 straight x plus 5 space equals space 1
III. space straight x squared minus 5 straight x space plus 5 space equals space minus 1 space and space straight x squared plus 4 straight x minus 60 space equals space Even

Case space straight I space when space straight x squared space plus space 4 space straight x minus 60 space equals space 0 comma space then
straight x squared space plus space 10 space straight x space minus 6 straight x space minus 60 equals 0
rightwards double arrow space straight x left parenthesis straight x plus 10 right parenthesis minus 6 left parenthesis straight x plus 10 right parenthesis space equals space 0
rightwards double arrow left parenthesis straight x plus 10 right parenthesis left parenthesis straight x plus 6 right parenthesis space equals space 0
rightwards double arrow straight x space equals space minus space 10 space or space straight x equals space 6
Note space that comma space for space these space two space vaues space of space straight x comma space straight x squared minus 5 straight x space plus space 5 space not equal to 0
Case space II space when space straight x squared space minus 5 straight x space plus 5 space equals space 1
straight x squared space minus 5 straight x space plus 4 space equals space 0
straight x squared minus 4 straight x minus straight x space plus 4 equals 0
straight x left parenthesis straight x minus 4 right parenthesis minus 1 left parenthesis straight x minus 4 right parenthesis space equals 0
left parenthesis straight x minus 4 right parenthesis left parenthesis straight x minus 1 right parenthesis space equals 0
straight x equals space 4 space or space straight x space equals 1

Case space III space when space straight x squared minus 5 straight x space plus 5 space equals space minus 1
straight x squared minus 5 straight x space plus 5 space equals space minus 1
straight x squared minus 5 straight x space plus space 6 space equals space 0
rightwards double arrow space straight x squared minus 2 straight x minus 3 straight x space plus 6 space equals space 0
straight x left parenthesis straight x minus 2 right parenthesis minus 3 left parenthesis straight x minus 2 right parenthesis space equals space 0
left parenthesis straight x minus 2 right parenthesis left parenthesis straight x minus 3 right parenthesis space equals 0
straight x equals 2 space or space straight x space equals space 3
Now comma space when space straight x space equals space 2 comma space straight x to the power of 2 space end exponent plus 4 straight x minus 60 space equals space 4 plus 8 minus 60
equals negative 48 comma space which space is space an space interger
when space straight x space equals space 3 comma space straight x squared plus space 4 straight x space minus 60 space equals space 9 space plus 12 minus 60 space equals space minus 39
which space is space not space an space even space interger.
Thus comma space in space this space case comma space we space get space straight x space equals space 2
Hence comma space the space sum space of space all space real space values space of space
straight x space equals space minus 10 plus 6 plus 4 plus 1 plus 2 space equals 3

Sponsor Area

Question
CBSEENMA11015446

If all the words (with or without meaning) having five letters, formed using the letters of the word SMALL and arranged as in a dictionary; then the position of the word SMALL is:

  • 46th

  • 59th

  • 52nd

  • 58th

Solution

D.

58th

Clearly, number of words start with A = 4!/ 2! = 12
Number of words start with L = 4! = 24
A number of words start with M = 4!/2! = 12
Number of words start with SA = 3!/2! = 3
Number of words starts with SL = 3! = 6
Note that, next word will be 'SMALL'
Hence, the position of word 'SMALL' is 58th.

Question
CBSEENMA11015447

If the number of terms in the expansion of open parentheses 1 minus 2 over straight x space plus 4 over straight x squared close parentheses to the power of straight n comma straight x not equal to 0 comma is 28, then the sum of the coefficients of all the terms in this expansion is

  • 64

  • 2187

  • 243

  • 729

Solution

D.

729

Clearly, number of terms in the expansion of 

open parentheses 1 minus 2 over straight x plus 4 over straight x squared close parentheses space is space fraction numerator left parenthesis straight n plus 2 right parenthesis left parenthesis straight n plus 1 right parenthesis over denominator 2 end fraction space or space straight C presuperscript straight n plus 2 end presuperscript subscript 2
left square bracket assuming space 1 over straight x space and space 1 over straight x squared space distinct right square bracket
therefore comma space fraction numerator left parenthesis straight n plus 2 right parenthesis left parenthesis straight n plus 1 right parenthesis over denominator 2 end fraction space equals space 28
rightwards double arrow space left parenthesis straight n plus 2 right parenthesis left parenthesis straight n plus 1 right parenthesis space equals space 56 space
space equals space left parenthesis 6 plus 1 right parenthesis left parenthesis 6 plus 2 right parenthesis space rightwards double arrow straight n space equals space 6
Hence comma space sum space of space coefficients equals space left parenthesis 1 minus 2 plus 4 right parenthesis to the power of 6 space equals space 3 to the power of 6 space equals space 729

Question
CBSEENMA11015448

If the 2nd, 5th and 9th terms of a non-constant A.P. are in G.P., then the common ratio of this G.P. is:

  • 8/5

  • 4/3

  • 1

  • 7/4

Solution

B.

4/3

Let a be the first term and d be a common difference. Then, we have a+d, a+4d, a+8d in GP,
ie. (a +4d)2 = (a+d)(a+8d)
⇒ a2 +16d2 +8ad = a2 +8ad +ad +8d2
⇒ 8d2 = ad
8d =a  [∴ d≠0]
Now, common ratio,
fraction numerator straight a plus 4 straight d over denominator straight a plus straight d end fraction space equals space fraction numerator 8 straight d space plus 4 straight d over denominator 8 straight d space plus straight d end fraction space equals space fraction numerator 12 straight d over denominator 9 straight d end fraction space equals space 4 over 3

Question
CBSEENMA11015449

If the sum of the first ten terms of the series,

open parentheses 1 3 over 5 close parentheses squared space plus open parentheses 2 2 over 5 close parentheses squared space plus open parentheses 3 1 fifth close parentheses squared space plus space 4 squared space plus space open parentheses 4 4 over 5 close parentheses squared space plus.....is 16/5 m, the m is equal to

  • 102

  • 101

  • 100

  • 99

Solution

B.

101

Let S10 be the sum of first ten terms of the series. Then, we have

S subscript 10 space equals open parentheses 1 3 over 5 close parentheses squared space plus open parentheses 2 2 over 5 close parentheses squared space plus open parentheses 3 1 fifth close parentheses squared space plus space 4 squared space plus space open parentheses 4 4 over 5 close parentheses squared space plus..... space to space 10 space terms
equals open parentheses 8 over 5 close parentheses squared space plus open parentheses 12 over 5 close parentheses squared space plus open parentheses 16 over 5 close parentheses squared space plus 4 squared space plus open parentheses 24 over 5 close parentheses squared space plus.... space to space 10 space terms
equals 4 squared over 5 squared space left parenthesis 2 squared space plus 3 squared plus 4 squared space plus 5 squared plus........ space to space 10 space terms right parenthesis
equals 4 squared over 5 squared space left parenthesis 2 squared space plus 3 squared plus 4 squared space plus 5 squared plus...11 squared right parenthesis
equals space 16 over 25 space left parenthesis 1 squared space plus 2 squared space plus..... plus 11 squared right parenthesis minus 1 squared right square bracket

equals 16 over 25 space open parentheses fraction numerator 11. left parenthesis 11 plus 1 right parenthesis left parenthesis 2.11 plus 1 right parenthesis over denominator 6 end fraction minus 1 close parentheses
space equals space 16 over 25 left parenthesis 506 minus 1 right parenthesis space equals space 16 over 25 space straight x space 505
rightwards double arrow 16 over 5 space straight m space equals space 16 over 25 space straight x space 505
straight m space equals space 101