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SSC Selection Post 2019 PYQ — Question 64

SSC Selection Post - Graduation Level 2019 - 15 Oct 2019 • Quantitative Aptitude • Q64

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If x−1x=7x-\frac{1}{x}=7, then what is the value of (x3−1x3)\left ( x^3-\frac{1}{x^3} \right )?

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Correct answer: D

Explanation

The correct answer is Option 4 i.e.  364.

If a - 1/a = b then a3 - 1/a3 = b3 + 3b

x - 1/x = 7

⇒ x3 - 1/x3 = 73 + 3(7) = 343 + 21 = 364