Q30 / 54 · JEE Advanced 2017 (Paper 1) · Mathematics

Let f : R→R be a differentiable function such that f0=0, fπ2=3 and f′0=1. If gx=∫xπ2 f′tcosect-cott cosect ftdt , for x∈0,π2 then limx→0⁡gx=

Correct answer: 2

Solution

g(x)= ∫xπ2[f'(t)cosec t−f(t)cosec t cot t]dt

=f(t)cosectxπ2

=fπ2cosec π2-fxsin⁡x=3-fxsin⁡x

∴     limx→0⁡gx=3-limx→0⁡fxsin⁡x=limx→0⁡f'xcos⁡x; as f'0=1

⇒    limx→0⁡gx=3-1=2

Hence, the correct answer is 2.

Relevant Questions