1.

Mark (√) against the correct answer in the following: Let f : N → X : f(x) = 4x2 + 12x + 15. Then, f-1(y) = ?A. \(\frac{1}{2}(\sqrt{y-4}+3)\) B. \(\frac{1}{2}(\sqrt{y-6}-3)\)C. \(\frac{1}{2}(\sqrt{y-4}+5)\)D. None of these

Answer»

Correct Answer is (B) \(\frac{1}{2}(\sqrt{y-4}+3)\)

f(x) = 4x2 + 12x + 15

⇒y = 4x2 + 12x + 15

⇒y = (2x + 3)2 + 6

⇒√(y - 6) = 2x + 3

⇒ \(\frac{1}{2}(\sqrt{y-4}+3)\) = x

f-1(y) =\(\frac{1}{2}(\sqrt{y-4}+3)\)



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