Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Definite Integration

Question:
What is $\int_{0}^{\pi/4}\log(1+\tan x)dx$?
Options:
1
$(\pi/4)\log3$
$(\pi/8)\log 2$
$\pi/2$
Correct Answer:
$(\pi/8)\log 2$
Explanation:
Using ,$\int_{0}^{a}f(x)dx$=$\int_{0}^{a}f(a-x)dx$ we get $I=\int_{0}^{\pi/4}\log(1+\tan (\pi/4-x))dx=\int_{0}^{\pi/4}\log(2/1+tan x)dx$. From this we can write $2I=[x\log 2](\pi/4)-[x\log 2](0)$. Hence $I=\pi/8\log 2$