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Math Help - integral issue with ln

  1. #1
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    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.
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  2. #2
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    Re: integral issue with ln

    you're integrating \frac{u'}{u} ... what is the derivative of (30-A) ?
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  3. #3
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    Re: integral issue with ln

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