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Math Help - simple complex numbers proof

  1. #1
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    simple complex numbers proof

    If z = cisΘ, show that cos(nΘ) = 1/2 (z^n + (1/z^n))

    I have done:

    z^n = (cisΘ)^n = cos(nΘ) + isin(nΘ)

    cos(nΘ) = z^n - isin(nΘ)

    Don't know where to go from here. Any help or advice would be greatly appreciated.
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  2. #2
    Super Member Matt Westwood's Avatar
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    Now do z^{-n} and add it to what you've already got.
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  3. #3
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    I've got it now =]
    Thank you very much
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