[tex]\int x^2\sqrt{(x^2-4)} dx[/tex]

The evaluation is clear (from an old

*Table of Integrals*I found), but the derivation is not at all clear, which is what i want to know.

I also tried to solve this by integration by parts, but every approach ended with an even more complicated integral, so trig substitution is probably the best choice.

Can anyone help?