# integral issue with ln

• October 17th 2011, 03:03 PM
satis
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:

$\int{\frac{1}{30-A}dA}$ which to me is pretty straight-forward as just $ln|30-A|$. For some reason, the book says the answer is $-ln|30-A|$. Can someone explain where the negative came from?

I can post the full problem if that's important.
• October 17th 2011, 03:08 PM
skeeter
Re: integral issue with ln
you're integrating $\frac{u'}{u}$ ... what is the derivative of (30-A) ?
• October 17th 2011, 03:30 PM
satis
Re: integral issue with ln
oh.... ok, I got it, thanks.
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