1)

$\int \frac{dx}{\cos x+\sqrt{3}sin x}$  equals


A) $\frac{1}{2}\log \tan (\frac{x}{2}+\frac{\pi}{12})+C$

B) $\frac{1}{3}\log \tan (\frac{x}{2}-\frac{\pi}{12})+C$

C) $\log \tan (\frac{x}{2}+\frac{\pi}{6})+C$

D) $\frac{1}{3}\log \tan (\frac{x}{2}-\frac{\pi}{6})+C$

Answer:

Option A

Explanation:

$\int \frac{dx}{\cos x+\sqrt{3}sin x}$

= $\frac{1}{2}\int \frac{dx}{\frac{1}{2}\cos x+\frac{\sqrt{3}}{2}sin x}$

=$\frac{1}{2}\int \frac{dx}{\cos\frac{\pi}{3}\cos x+\sin\frac{\pi}{3}sin x}$

=  $\frac{1}{2}\int \frac{dx}{\cos(x-\frac{\pi}{3})}$

   =$\frac{1}{2}\int \sec (x-\frac{\pi}{3}) dx$

=$\frac{1}{2}\log \tan (\frac{x}{2}-\frac{\pi}{6}+\frac{\pi}{4})+C$

  = $\frac{1}{2}\log \tan (\frac{x}{2}+\frac{\pi}{12})+C$