NTA Abhyas JEE Main2020MathematicsApplication of DerivativesPractice
A differentiable function f x satisfies f 0 = 0 and f 1 = sin 1 , then (where f ' represents derivative of f )
Options
- Af ' c = cos c ,   ∀ c ∈ 0 , 1
- Bf ' c = cos c for some c ∈ 0 , 1
- Cf ' c = − cos c ,   ∀ c ∈ 0 , 1
- Df ' c = 2 cos c ,   ∀ c ∈ 0 , 1
Correct answer
B. f ' c = cos c for some c ∈ 0 , 1
Step-by-step solution
Let, g x = f x - sin ⁡ x Now, g 0 = f 0 - 0 = 0 & g 1 = f 1 - sin ⁡ 1 = 0 As g x is differentiable, so by Rolle’s theorem, g ′ c = 0 for some c ∈ 0,1 i.e. f ′ c − cos c = 0 ⇒ f ′ c = cos c   for   some   c ∈ 0 , 1