Let f and g be differentiable functions on R such that f o g is the identity function. If for some a , b…

Let f and g be differentiable functions on R such that fog is the identity function. If for some a,b∈R,g'a=5 and ga=b, then f'b is equal to:
  1. 15
  2. 1
  3. 5
  4. 25

Solution

fgx=x

⇒f'gx.g'x=1

Put x=a

⇒f'gag'a=1

⇒f'b×5=1

⇒f'b=15

Asked in: JEE Main 2020 (09 Jan Shift 2)

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