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SSC Selection Post 2020 PYQ — Question 54

SSC Selection Post - Graduation Level 2020 - 9 Nov 2020 - Shift 2 • Quantitative Aptitude • Q54

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If x3+y3x ^ 3 + y ^ 3 = 175 and x + y = 7 , find the value of x4+y4x ^ 4 + y ^ 4 .

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Correct answer: A

Explanation

The correct answer is Option 1 i.e. 961.

x3 + y3 = (x + y)3 - 3xy(x + y)

⇒ 175 = 73 - 21xy

⇒ 175 = 343 - 21xy

⇒ xy = 8

(x + y)2 = x2 + y2 + 2xy

⇒ 49 = x2 + y2 + 16

⇒ x2 + y2 = 33

⇒ (x2 + y2)2 = 1089

⇒ x4 + y4 + 2x2y2 = 1089

⇒ x4 + y4 + 2(64) = 1089

⇒ x4 + y4 = 1089 - 128 = 961