MCQ
Evaluate: $\int_0^{\pi / 4} \tan ^3 x d x$
  • A
    $(1-\log 2)$
  • B
    $(1+\log 2)$
  • $\frac{1}{2}(1-\log 2)$
  • D
    $\frac{1}{2}(1+\log 2)$

Answer

Correct option: C.
$\frac{1}{2}(1-\log 2)$
(c)
$\begin{aligned}
\text { : Let } I= & \int_0^{\pi / 4} \tan ^3 x d x=\int_0^{\pi / 4}\left(\sec ^2 x-1\right) \tan x d x \\
& =\int_0^{\pi / 4} \sec ^2 x \tan x d x-\int_0^{\pi / 4} \tan x d x
\end{aligned}
$
Put $\tan x=t$ in first integral $\Rightarrow \sec ^2 x d x=d t$
When
$
\begin{array}{l}
x=0 \quad \Rightarrow t=0 \\
\therefore x=\pi / 4 \Rightarrow t=1 \\
I=\int_0^1 t d t-\int_0^{\pi / 4} \tan x d x=\left[\frac{t^2}{2}\right]_0^1-[\log |\sec x|]_0^{\pi / 4} \\
=\left(\frac{1}{2}-0\right)-\log \left|\sec \frac{\pi}{4}\right|+\log |\sec 0|=\frac{1}{2}(1-\log 2) \\
\end{array}
$

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