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SSC Selection Post 2022 PYQ — Question 75

SSC Selection Post - Higher Secondary Level - 09 Feb 2022 - Shift 2 • Quantitative Aptitude • Q75

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If 2x2 + 5x + 1 = 0, then one of the values of 12(x−12x){1 \over 2} ({x - {1 \over 2x}}) is :

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Correct answer: B

Explanation

The correct answer is option 2 i.e. 172{\sqrt{17} \over 2}.

2x2 + 5x + 1 = 0

Divide the equation by 2x

⇒ x + 5x2x5x\over2x + 12x1\over2x = 0

⇒ x + 12x1\over2x = -525\over2

Uing formuale: (a - b)2 = (a + b)2 - 4ab

⇒ (x - 12x1\over2x)2 = (x + 12x1\over2x)2 - 4 × x × 12x1\over2x

⇒ (x - 12x1\over2x)2 = (-525\over2)2 - 2

⇒ (x - 12x1\over2x)2 = 25425\over4 - 2

⇒ (x - 12x1\over2x) = 174\sqrt{17\over4} = 172{\sqrt{17} \over 2}