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SSC Selection Post 2019 PYQ — Question 56

SSC Selection Post - Matriculation Level 2019 - 14 Oct 2019 - Shift 1 • Quantitative Aptitude • Q56

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 If x- x-1 = 6, then the value of x4 + x-4 is:

 

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Correct answer: D

Explanation

The correct answer is Option 4 i.e. 1442

x−1x=6x - \frac{1}{x} = 6

(x−1x)2=x2+1x2−2=36\left(x - \frac{1}{x}\right)^2 = x^2 + \frac{1}{x^2} - 2 = 36

x2+1x2=38x^2 + \frac{1}{x^2} = 38

(x2+1x2)2=x4+1x4+2=382=1444\left(x^2 + \frac{1}{x^2}\right)^2 = x^4 + \frac{1}{x^4} + 2 = 38^2 = 1444

⇒x4+1x4=1444−2=1442\Rightarrow x^4 + \frac{1}{x^4} = 1444 - 2 = 1442