Answer
$\sin^{-1} x+C$
Work Step by Step
Consider $x=\sin \theta \implies dx= \cos \theta d \theta $
Now, the given integral can be written as:
$\int\dfrac{\cos \theta}{ \sqrt{1-\sin^2 \theta}} d\theta= \int \dfrac{\cos\theta}{\sqrt {\cos^2 \theta}}$
or, $= \int d \theta$
or, $=\sin^{-1} x+C$
