Please help. I don't know how to deal with this integral $$\displaystyle\int_0^{\pi/2}\frac{\cos^2x}{a\cos^2x + b\sin^2x}\,dx$$ I reached the step
$$=\displaystyle\ \int_0^{\pi/2}\frac{\sec^2 x}{\sec^2 x}\cdot \frac{\cos^2x}{a\cos^2x + b\sin^2x}dx$$
$$=\displaystyle\ \int_0^{\pi/2}\frac{1}{a + b\tan^2x}dx$$
Now what should I do?