$ Let \, \, I = \int^{ \pi / 2 }_ 0 \frac {\sqrt { cot \, x }}{ \sqrt { cot \, x } + \sqrt { tan \, x }} \, dx \, is ..................(1)$
$ \Rightarrow \, \, I = \int^{ \pi / 2 }_ 0 \frac {\sqrt { tan \, x }}{ \sqrt { cot \, x } + \sqrt { tan \, x }} \, dx \, is ..................(2)$
On adding Eqs. (i) and (ii), we get
$ 2I = \int^{ \pi / 2 }_ 0 \, 1 \, dx $
$ \therefore I = \frac{\pi}{4 } $