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SSC CHSL 2019 PYQ — Question 54

SSC CHSL - 1st July 2019 - Shift 3 • Quantitative Aptitude • Q54

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If 8x2 + y2 – 12x – 4xy + 9 = 0 then the value of (14x – 5y) is:

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Correct answer: C

Explanation

The Correct Answer is option 3 i.e. 6

Application

Given

8x2 + y2 – 12x – 4xy + 9 = 0

We will try the make the perfect squares:

8x2 + y2 – 12x – 4xy + 9 = 0

⇒ 4x2 + y2 – 4xy + 4x2 – 12x + 9 = 0

⇒ (2x – y)2 + (2x – 3)2 = 0

⇒ x = y/2 and x = 3/2

Hence, y = 2x = 3

14x – 5y

= 14 × 3/2 - 5 × 3

= 21 – 15 = 6