# Integration Problem

Hi! Could someone give me an idea how the following integration be carried out??

$$\int \frac{r dr}{ \left( r^2 + a^2 - 2rau \right)^{3/2}} = \frac{ru - a}{a(1-u^2)\sqrt{r^2 + a^2 - 2rau}}$$

where u and a are constant.

I have encounter such integration several times in electrodynamics.

I can solve it in lengthy way, but can't carry out such compact result as above. Could someone help me?? Thanks a lot!!