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Homework Help: Fourier series-desperately needing help

  1. Sep 13, 2007 #1
    fourier series--desperately needing help

    1. The problem statement, all variables and given/known data

    2. Relevant equations

    in the a[tex]_{n}[/tex] on the fifth equal sign, why was (-1 ^n)? how did he arrive at that equation?

    have mercy..
    its our quiz today
    and i really have a hard time on fourier

    3. The attempt at a solution
  2. jcsd
  3. Sep 13, 2007 #2
    cos (\pi n) for n = even integer is equal to 1,
    while for n = odd inetger, it is equal to -1.
    The function (-1)^n has the same property.
    Since n is an integer and must be either even or odd,
    we can replace cos (\pi n) with (-1)^n .
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