Different substitutions
a. Show that $\int \frac{d x}{\sqrt{x-x^{2}}}=\sin ^{-1}(2 x-1)+C$ using either
$u=2 x-1$ or $u=x-\frac{1}{2}$
b. Show that $\int \frac{d x}{\sqrt{x-x^{2}}}=2 \sin ^{-1} \sqrt{x}+C$ using $u=\sqrt{x}$
c. Prove the identity $2 \sin ^{-1} \sqrt{x}-\sin ^{-1}(2 x-1)=\frac{\pi}{2}$
(Source: The College Mathematics Journal 32, 5, Nov 2001)