Using differentiation under integral sign evaluate $\int_{0}^{\frac {\pi}{2}} \ln (\frac {a+b\sin x}{a-b\sin x}) \cdot \frac {dx}{\sin x} $
Evaluate integral $\int_0^\frac{\pi}{2} \ln\left(\frac{1+a\cos x}{1-a\cos x}\right) \frac{\mathrm{d} x}{\cos x}$ for $\left|a\right|<1$