Latest SSC Aptitude Question SOLUTION: If x^4+1/x^4=119, then the value of x^3-1/x^3 is a)+ or - 36 b) + or - 33 c)36 d) -36

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(#M40109387) SSC Numerical Ability question Keep an EYE

If x^4+1/x^4=119, then the value of x^3-1/x^3 is
a)+ or - 36 b) + or - 33 c)36 d) -36

Asked In SSC Meenakshi (9 years ago)

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Sudipta Kumar Banerjee  (9 years ago)

x^4 + 1/x^4 = 119
or, (x^2+1/x^2)^2 - 2 = 119
or, (x^2+1/x^2)^2 = 121
or, x^2+1/x^2 = 11 [considering +ve value]
or, (x - 1/x)^2 +2 = 11
or, (x - 1/x)^2 = 9
or, x - 1/x = +-3

Now, x^3 - 1/x^3
=(x - 1/x)^3 + 3*x*1/x*(x - 1/x)
=(3)^3 + 3 * 3 or, =(-3)^3 + 3*(-3)
=27 + 9 =-27 - 9
=36 = -36

so Ans: a) + or - 36

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