Let ƒ and g be differentiable functions on R such that fog is the identity function. If for some a, b $\in$ R, g'(a) = 5 and g(a) = b, then ƒ'(b) is equal to :
Solution
Given the function composition f(g(x)) is the identity function, it means f(g(x)) = x for all x.
<br><br>$\Rightarrow$ ƒ'(g(x)) g'(x) = 1
<br><br>put x = a
<br><br>$\Rightarrow$ ƒ'(b) g'(a) = 1
<br><br>$\Rightarrow$ ƒ'(b) = ${1 \over 5}$
About this question
Subject: Mathematics · Chapter: Differentiation · Topic: Chain Rule
This question is part of PrepWiser's free JEE Main question bank. 55 more solved questions on Differentiation are available — start with the harder ones if your accuracy is >70%.