JEE Main2014MathematicsFunctionsActual
If g is the inverse of a function f and f ' x = 1 1 + x 5 , then g ' x is equal to
Options
- A1 1 + g x 5
- B1 + g x 5
- C1 + x 5
- D5 x 4
Correct answer
B. 1 + g x 5
Step-by-step solution
g is the inverse of f i.e. g x = f - 1 x   ⇒ f g x = x Differentiating both the sides w.r.t x , we get f ' g x . g ' x = 1 ⇒ g ' x = 1 f ' g x as   f ' x = 1 1 + x 5 ⇒ g ' x = 1 1 1 + g x 5   g ' x = 1 + g x 5