For definite integrals involving $\sqrt{1-x^2}$, the substitution $x=\sin\theta$ or $x=\cos\theta$ is standard. Remember the important definite integral results: $\int_0^{\pi/2} \log(\sin x) dx = \int_0^{\pi/2} \log(\cos x) dx = -\frac{\pi}{2}\log 2$.