# Homework Help: Integrating by parts

1. Nov 9, 2011

### AnnieF

1. The problem statement, all variables and given/known data

∫r^3/(4+r^2)^(1/2) dr

2. Relevant equations

∫udv=uv-∫vdu

3. The attempt at a solution

I know that integration by parts must be used. I tried doing it with 4+r^2 as u, but kept running into issues..then I got an answer but it appears to be wrong. I guess I am not sure how to do this.

2. Nov 9, 2011

### ehild

First substitute r^2=t, then integrate by parts.

ehild

3. Nov 9, 2011

### Dick

I don't think it needs integration by parts. I'd do a simple u substitution. u=r^2+4, like AnnieF suggested. What 'issues' were you running into?

4. Nov 10, 2011

### lineintegral1

The substitution $u=r^2$ would be significantly easier to deal with. One can then use parts or another substitution to make the integral elementary.