help with integration by substitution

[lightweight]

Hi,

I'm trying to help a friend with a calculus problem, but having a problem with it. I haven't done calculus since my freshman year in college. The problem is:
(x+ 3) / (x^2 + 6x)^2

I'm trying to integrate via substitution. Can someone show me how to properly do this? I looked on google, and had some problems understanding some of the pages that explained it.

 

[Fenixgoon]

multiply (x+3) by 2.. you get 2x + 6, which is the derivative of the bottom thing... let "A" = x^2 +6x, so dA = 2x + 3... dA/A^2, much easier to solve

 

[hypn0tik]

Consider u = x^2 + 6x

Then: du = (2x + 6)dx

0.5du = (x+3) dx

Now substitute in for x^2 + 6x and (x+3) dx and you're good to go.