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Math Help - algebra subs with e^x

  1. #1
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    sthlm
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    algebra subs with e^x

    Why can't I make the substitution
    -e^{-(x+y)}  \cdot -1 = e^{-(x+y)}?

    (See calculation here https://dl.dropbox.com/u/586465/Phot...%2017%2040.jpg I had to find ∂f/∂x=0 and I thought x=-1 but the book says x=1.
    Last edited by jacob93; September 13th 2012 at 03:25 AM.
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  2. #2
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    Re: algebra subs with e^x

    You should not have two minuses in your third line.
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  3. #3
    Junior Member
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    Re: algebra subs with e^x

    yes, since I have rewritten to e^minus, the inner derivative should be 1, not -1. Thanks.
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