To handle such 'troublesome' integral , first thing to do is to reduce it to a simplier form :
Let the integral becomes
it looks better now and we wish to obtain a reduction formula .
Use integration by parts ,
If , the reduction only consists of two variables but in general , it consists of three variables : , that means we have to find . By substituting we obtain :
I give you the case for , in the above expression , we asumme .
If you know the sign of , you should be able to continue ...