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SSC CHSL 2023 PYQ — Question 57

SSC CHSL 2023 - 04 Aug 2023 - Shift 3 • Quantitative Aptitude • Q57

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If (y - 1y\frac{1}{y}) = 9, find the value of (y³ -1y3\frac{1}{y^3}).

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Correct answer: B

Explanation

The correct answer is Option 2 i.e. 756.

(x3 - y3) = (x - y)3 + 3xy(x - y)

put x = y and y = 1/y

⇒ (y3 - 1/y3) = (y - 1/y)3 + 3 × y × 1/y(y - 1/y)

⇒ (y3 - 1/y3) = (9)3 + 3(9)

⇒ (y3 - 1/y3) = 729 + 27

⇒ (y3 - 1/y3) = 756