MCQ
$\int_{\pi /6}^{\pi /3} {\frac{{dx}}{{1 + \sqrt {\tan x} }} = } $
  • $\pi /12$
  • B
    $\pi /2$
  • C
    $\pi /6$
  • D
    $\pi /4$

Answer

Correct option: A.
$\pi /12$
a
(a) $I = \int_{\pi /6}^{\pi /3} {\frac{{dx}}{{1 + \sqrt {\tan x} }}} $

$ = \int_{\pi /6}^{\pi /3} {\frac{{\sqrt {\cos x} }}{{\sqrt {\cos x} + \sqrt {\sin x} }}\;dx} $ ..$(i)$

$I = \int_{\pi /6}^{\pi /3} {\frac{{\sqrt {\sin x} }}{{\sqrt {\cos x} + \sqrt {\sin x} }}\;} $ ..$(ii)$

(Since $\int_a^b {f(x)dx} = \int_a^b {f(a + b - x)\,dx} $)

Adding $(i)$ and $(ii),$ we get, 

$2I = \int_{\pi /6}^{\pi /3} {\;dx} $

==> $I = \frac{1}{2}\left( {\frac{\pi }{3} - \frac{\pi }{6}} \right) = \frac{\pi }{{12}}$.

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