MCQ
$\int_0^{\pi / 6} \frac{\sin x}{\cos ^3 x} d x=$
  • A
    $\frac{2}{3}$
  • $\frac{1}{6}$
  • C
    2
  • D
    $\frac{1}{3}$

Answer

Correct option: B.
$\frac{1}{6}$
(B)
Let $I =\int_0^{\pi / 6} \frac{\sin x}{\cos ^3 x} d x=\int_0^{\frac{\pi}{6}} \tan x \sec ^2 x d x$
Put $\tan x= t \Rightarrow \sec ^2 x d x= dt$
When $x=0, t =0$ and when $x=\frac{\pi}{6}, t =\frac{1}{\sqrt{3}}$
$\therefore \quad I =\int_0^{\frac{1}{3}} tdt =\left[\frac{ t ^2}{2}\right]_0^{\frac{1}{\sqrt{3}}}=\frac{1}{6}$

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