calculus - Definite integration evaluation of $int_0^{pi/2} frac{sin^2(x)}{(b^2cos^2(x)+a^2 sin^2(x))^2}~dx$.

$$\int_0^{\pi/2} \frac{\sin^2(x)}{(b^2\cos^2(x)+a^2 \sin^2(x))^2}~dx$$

how to proceed please help

The answer given is $\dfrac{\pi}{4a^3b}$.