Thread: integral issue with ln

This is part of a larger mixing problem, but I'm confused with this particular part. I got to an integral of:

which to me is pretty straight-forward as just . For some reason, the book says the answer is . Can someone explain where the negative came from?

I can post the full problem if that's important.

you're integrating ... what is the derivative of (30-A) ?

oh.... ok, I got it, thanks.