Question
$$\int {\sqrt {\frac{x}{{1 - x}}} } dx$$ is equal to :
A.
$${\sin ^{ - 1}}\sqrt x + c$$
B.
$${\sin ^{ - 1}}\left\{ {\sqrt x - \sqrt {x\left( {1 - x} \right)} } \right\} + c$$
C.
$${\sin ^{ - 1}}\sqrt {x\left( {1 - x} \right)} + c$$
D.
$${\sin ^{ - 1}}\sqrt x - \sqrt {x\left( {1 - x} \right)} + c$$
Answer :
$${\sin ^{ - 1}}\sqrt x - \sqrt {x\left( {1 - x} \right)} + c$$
Solution :
$$\eqalign{
& {\text{Put }}x = {\sin ^2}\theta \Rightarrow dx = 2\,\sin \,\theta \,\cos \,\theta \cr
& \therefore \,\int {\sqrt {\frac{x}{{1 - x}}} dx} \cr
& = \int {\frac{{\sin \,\theta }}{{\cos \,\theta }}.2\,\sin \,\theta \,\cos \,\theta } \,d\theta \cr
& = \int {\left( {1 - \cos \,2\theta } \right)} d\theta \cr
& = \theta - \frac{1}{2}\sin \,2\theta + c \cr
& = {\sin ^{ - 1}}\sqrt x - \sqrt {x\left( {1 - x} \right)} + c \cr} $$