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SSC Selection Post 2019 PYQ — Question 73

SSC Selection Post - Higher Secondary Level - 16 Oct 2019 - Shift 2 • Quantitative Aptitude • Q73

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​If x8 - 727x4 + 1 = 0, then the possible value of x−1xx - {1 \over x} is:   

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Correct answer: C

Explanation

The correct answer is option 3 i.e. 5.

Given, x8 - 727x4 + 1 = 0

Divide the given equation by x4, x4 + 1/x4 = 727

Now, add 2 on both sides, x4 + 1/x4 + 2 = 729

⇒ (x2 + 1/x2)2 = 729

⇒ (x2 + 1/x2) = 27

Now, subtract 2 from both sides, x2 + 1/x2 - 2 = 25

⇒ (x - 1/x)2 = 25

⇒ x - 1/x = 5