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Math Help - Can't evaluate this integral

  1. #1
    Junior Member
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    Feb 2009
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    Can't evaluate this integral

    I can't follow a proof in my physics class. It involves this:
    \int^{2pi}_0 e^{i(n+1)x}dx
    I am suppose to get 2pi for n=-1 and 0 otherwise.
    I got:
    \frac{e^{i(n+1)x}}{i(n+1)}
    Using euler's formula I got:
    \frac{sin[(n+1)x]}{n+1}-i \frac{[cos(n+1)x]}{n+1}
    Pluging in the limits I only got 0 regardless of what n is.
    What am I missing?
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  2. #2
    Senior Member Sampras's Avatar
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    For n = -1, the integral is  \int_{0}^{2 \pi} 1 \ dx = 2 \pi .
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  3. #3
    Junior Member
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    OMG........thank.... I spent so long working blind....... I was trying to plug in n after I do the work.
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