Just evaluate the integral...

$\displaystyle \int_{0}^{1/2}\sin^{-1}{x} dx$

I used...

$\displaystyle u=\sin^{-1}{x}$

$\displaystyle du=\frac{dx}{\sqrt {1-x^2}}$

$\displaystyle dv=dx$

$\displaystyle v=x$

The problem is that I get stuck with $\displaystyle \int_{0}^{1/2}\frac{xdx}{\sqrt {1-x^2}}$ eventually and I'm not quite sure where to go with it. I thought of maybe doing a sub, but I'm not sure what to sub for.