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

Answer

Correct option: B.
$\frac{1}{6}$
b
(b) Let $I = \int_0^{\pi /6} {\frac{{\sin x}}{{{{\cos }^3}x}}dx = \int_0^{\pi /6} {\,\tan x{{\sec }^2}x\,dx} } $

Put $t = \tan x $

$\Rightarrow dt = {\sec ^2}x\,dx,$ then we have

$I = \int_0^{\frac{1}{{\sqrt 3 }}} {t\,dt = } \left[ {\frac{{{t^2}}}{2}} \right]_0^{\frac{1}{{\sqrt 3 }}} = \frac{1}{6}$.

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