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SSC Selection Post 2020 PYQ — Question 62

SSC Selection Post - Graduation Level 2020 - 9 Nov 2020 - Shift 2 • Quantitative Aptitude • Q62

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 If x = 3 + √8, find the value of x³ + 1x3\frac{1}{x^3}

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Correct answer: B

Explanation

The correct answer is Option 2 i.e. 198.

x = 3 + √8

⇒ 1/x = (3 - √8)/[(3 + √8)(3 - √8)] = 3 - √8

⇒ x + 1/x = (3 + √8) + (3 - √8) = 6

So, x3 + 1/x3 = (x + 1/x)3 - 3(x + 1/x)

= 63 - 3 × 6

= 216 - 18

= 198