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JEE Main20209 Jan 2020Evening ShiftMathematicsDifferentiationActual

Let f and g be differentiable functions on R such that f o g is the identity function. If for some a , b ∈ R , g ' a = 5 and g a = b , then f ' b is equal to:

Options

  1. A1 5
  2. B1
  3. C5
  4. D2 5

Correct answer

A. 1 5

Step-by-step solution

f g x = x ⇒ f ' g x . g ' x = 1 Put x = a ⇒ f ' g a g ' a = 1 ⇒ f ' b × 5 = 1 ⇒ f ' b = 1 5

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