Hi guys, I'm new on the forum and need a little assistance... we were given this to integrate:

/int x^3/sqrt (x^2+1)dx

And were instructed to integrate by trig integration and integration by parts and then show that they are the same. I got the answer with trig integration:

1/3 sqrt (x^2+1)^3 - 1/sqrt (x^2+1) + c

but I can't figure out how to do it by parts. What should I assign as u and dv and why?