MCQ
$\int_0^{\pi /2} {\frac{{\sqrt {\cot x} }}{{\sqrt {\cot x} + \sqrt {\tan x} }}\,dx = } $
  • A
    $\pi $
  • B
    $\frac{\pi }{2}$
  • $\frac{\pi }{4}$
  • D
    $\frac{\pi }{3}$

Answer

Correct option: C.
$\frac{\pi }{4}$
c
(c) $I = \int_0^{\pi /2} {\frac{{\sqrt {\cot x} }}{{\sqrt {\cot x} + \sqrt {\tan x} }}dx} $.....$(i)$

$ = \int_0^{\pi /2} {\frac{{\sqrt {\cot \left( {\frac{\pi }{2} - x} \right)} }}{{\sqrt {\cot \left( {\frac{\pi }{2} - x} \right)} + \sqrt {\tan \left( {\frac{\pi }{2} - x} \right)} }}dx} $

$ = \int_0^{\pi /2} {\frac{{\sqrt {\tan x} }}{{\sqrt {\tan x} + \sqrt {\cot x} }}dx} $.....$(ii)$

Now adding $(i)$ and $(ii),$ we get

$2I = \int_0^{\pi /2} {\frac{{\sqrt {\cot x} + \sqrt {\tan x} }}{{\sqrt {\tan x} + \sqrt {\cot x} }}dx = [x]_0^{\pi /2} \Rightarrow I = \frac{\pi }{4}} $.

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