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SSC CGL 2017 PYQ — Question 74

SSC CGL Tier II Quant - 12/01/2017 • Quantitative Aptitude • Q74

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If ax + by = 1 and bx + ay = 2ab/(a2 + b2) then (x2 + y2)(a2 + b2) is equal to:

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Correct answer: B

Explanation

  The correct answer is option 2 i.e. 2

Application

ax + by = 1 and bx + ay = 2ab/(a2 + b2)

Put x = 0 and y = 1

From the first equation:

0 + b = 1

⇒ b = 1

Put x = 0, y = 1 and b = 1 in 2nd equation:

0 + a = 2a/(a2 + 1)

⇒ a2 + 1 = 2

⇒ a2 = 1

⇒ a = 1

Now, put x = 0, y = 1, b = 1 and a = 1 in given equation:

⇒ (x2 + y2)(a2 + b2) = (0 + 1)(1 + 1) = 2