Question
Integrate the function: $\frac{\cos x}{\sqrt{4-\sin ^{2} x}}$

Answer

Let $I=\frac{\cos x}{\sqrt{4-\sin ^{2} x}}$ 
Put sin x = t ⇒ cos x dx = dt
$\Rightarrow \int \frac{\cos x}{\sqrt{4-\sin ^{2} x}} d x=\int \frac{1}{\sqrt{4-t^{2}}} d t$ 
$=\int \frac{1}{\sqrt{\left(2^{2}-t^{2}\right)}} d t$ 
= $\sin ^{-1}\left(\frac{t}{2}\right)+C$ 
$\Rightarrow I=\sin ^{-1}\left(\frac{\sin x}{2}\right)+C$

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