SarkariPYQ

SSC CHSL 2021 PYQ — Question 73

SSC CHSL - 12 April 2021 - Shift 3 • Quantitative Aptitude • Q73

Back to paper

If x4 + 1/x4 = 6887, then the positive value of x-1/x is:

Show answer & explanation

Correct answer: C

Explanation

The correct answer in option 3 i.e. 9

x4+1x4=6887\rm x^4+\frac{1}{x^4}=6887

By adding 2 on both sides. 

⇒ x4+1x4+2=6887+2\rm x^4+\frac{1}{x^4} +2=6887 +2

⇒(x2+1x2)2=6889(x^2 + \frac{1}{x^2})^2 = 6889

⇒(x2+1x2)=6889(x^2 + \frac{1}{x^2}) = \sqrt6889 = 83

Now, (x−1x)=(83−2)(x - \frac{1}{x}) = \sqrt(83-2) = 9