Why can't I make the substitution ? (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 04:25 AM.
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You should not have two minuses in your third line.
yes, since I have rewritten to e^minus, the inner derivative should be 1, not -1. Thanks.
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