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Math Help - fourier cosine series

  1. #1
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    fourier cosine series

    Hi, this question is being a pain to me can someone please help.

    a) Find the Fourier cosine series of f(x)=|sinx| for interval (-\pi, \pi).

    b) Use it to find the sum

    \sum_{n \ge 1} \frac{1}{4n^2-1}

    Thanks
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  2. #2
    Senior Member DeMath's Avatar
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    Re: fourier cosine series

    Use the standard formulas:

    Last edited by DeMath; October 14th 2011 at 06:46 AM. Reason: typo
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  3. #3
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    Re: fourier cosine series

    wow, thanks demath, I was just thrown a bit by the absolute sign. I understand it now.
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