# Integration By Parts: Need help with a step

1. Aug 2, 2009

### daviddee305

Integration By Parts: Need help with a step....

Evaluate the integral:

$$\int$$ ln(2x + 1)dx

I worked it out up until:

Xln(2x + 1) - $$\int$$ 2x/(2x + 1) dx

Then the next step throws me off. I attached a scan from the solutions manual and circled the part that confused me. Could somebody explain how we went from "2x/(2x + 1)" to "[(2x + 1) - 1]/(2x + 1)"?

I'm sure it's a simple arithmetic step I'm overlooking, which is why I'm reviewing a few weeks before Calc. 2.

2. Aug 2, 2009

### Cyosis

Re: Integration By Parts: Need help with a step....

Not much happens really, $(2x+1)-1=2x+1-1=2x$. As you can see both numerators are the same, the latter is just written in a more useful form.

3. Aug 2, 2009

### daviddee305

Re: Integration By Parts: Need help with a step....

thanks.... it makes sense now...