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Homework Help: Rewriting a symbolic Summation

  1. Apr 1, 2014 #1
  2. jcsd
  3. Apr 1, 2014 #2


    Staff: Mentor

    Pick a value for N, and expand the summation.
    Pick a different value for N, and expand the summation.
    After you do this a few times, maybe you can discover a pattern.
  4. Apr 1, 2014 #3

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    Standard method:
    [tex] \sum_{n=a}^{b} \cos(nw) = \frac{1}{2}\sum_{n=a}^{b} \left(e^{inw} + e^{-inw} \right)[/tex]
    This is a sum of two geometric series ##\sum r^n## with ##r = e^{iw}## and ##r = e^{-iw}##.
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