MCQ
$\int_0^{\pi / 4}(\sqrt{\tan x}+\sqrt{\cot x}) d x$ equals
  • A
    $\sqrt{2} \pi$
  • B
    $\frac{\pi}{2}$
  • $\frac{\pi}{\sqrt{2}}$
  • D
    $2 \pi$

Answer

Correct option: C.
$\frac{\pi}{\sqrt{2}}$
(C)
Let $I =\int_0^{\pi / 4}(\sqrt{\tan x}+\sqrt{\cot x}) d x$
$=\int_0^{\pi / 4} \frac{\sin x+\cos x}{\sqrt{\sin x \cos x}} d x$
$=\sqrt{2} \int_0^{\pi / 4} \frac{\sin x+\cos x}{\sqrt{1-(\sin x-\cos x)^2}} d x$
Put $\sin x-\cos x= t \Rightarrow(\cos x+\sin x) d x= dt$
$\therefore \quad I=\sqrt{2} \int_{-1}^0 \frac{ dt }{\sqrt{1- t ^2}}$
$\begin{array}{l}=\sqrt{2}\left[\sin ^{-1} t\right]_{-1}^0 \\ =\sqrt{2}\left[0-\left(\frac{-\pi}{2}\right)\right]=\frac{\pi}{\sqrt{2}}\end{array}$

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