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Math Help - polar form of complex number sign problem

  1. #1
    Junior Member
    Joined
    Nov 2008
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    polar form of complex number sign problem

    just got this worksheet back, and on this particular problem i'm told i messed up the negative/postive signs. I probably did...but i can't figure out how.

    ---

    12cis 210

    12(cos210 + i sin 210)

    (this next part is where i messed up the signs)

    12(sqrt3 /2 + i 1/2)

    answer: 6sqrt3 + 6i
    ---


    but doesn't cos 210deg = -sqrt3/-2? making it an overall positive?

    and same for the sin 210deg?
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  2. #2
    Super Member Deadstar's Avatar
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    cos 210 = - cos 30 = -sqrt(3)/2. Think of the cosine wave.
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