Medium MCQ +4 / -1 PYQ · JEE Mains 2022

Let f : R $\to$ R be defined as $f(x) = {x^3} + x - 5$. If g(x) is a function such that $f(g(x)) = x,\forall 'x' \in R$, then g'(63) is equal to ________________.

  1. A ${1 \over {49}}$ Correct answer
  2. B ${3 \over {49}}$
  3. C ${43 \over {49}}$
  4. D ${91 \over {49}}$

Solution

<p>$f(x) = 3{x^2} + 1$</p> <p>f'(x) is bijective function</p> <p>and $f(g(x)) = x \Rightarrow g(x)$ is inverse of f(x)</p> <p>$g(f(x)) = x$</p> <p>$g'(f(x))\,.\,f'(x) = 1$</p> <p>$g'(f(x)) = {1 \over {3{x^2} + 1}}$</p> <p>Put x = 4 we get</p> <p>$g'(63) = {1 \over {49}}$</p>

About this question

Subject: Mathematics · Chapter: Differentiation · Topic: Derivatives of Standard Functions

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