Definite Integration Question 378

Question: $ \int_0^{\pi /4}{{{\tan }^{6}}x{{\sec }^{2}}xdx=} $

[BIT Ranchi 1981]

Options:

A) $ \frac{1}{7} $

B) $ \frac{2}{7} $

C) 1

D) None of these

Show Answer

Answer:

Correct Answer: A

Solution:

Put $ t=\tan x\Rightarrow dt={{\sec }^{2}}xdx $

Now $ \int_0^{\pi /4}{{{\tan }^{6}}x{{\sec }^{2}}xdx=\int_0^{1}{t^{6}dt=\frac{1}{7}[t^{7}]_0^{1}=\frac{1}{7}}} $ .