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Complex analysis question (only need a hint)

  1. Jan 18, 2005 #1
    i know it's supposed to be a simple question. frustrating because it is not coming to me. just want a hint.

    question is:
    how do you write
    1 + cos(theta) + cos (2*theta) + cos(3*theta).... cos(n*theta) using the fact that (z^(n+1) -1) / (z^(n) -1) = 1 + z + z^(2) +... + z^(n)

    thanks in advance
  2. jcsd
  3. Jan 18, 2005 #2


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    Science Advisor
    Homework Helper

    How about
    [tex] Re \sum_{k=0}^{n} e^{ikz} [/tex]

    or sum over real of the same "animal"...Which one u prefer...??


    PS.Or theta,but it's cusomary to denote complex variables with "z"...
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