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Math Help - Hopefully last Polar question.

  1. #1
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    Hopefully last Polar question.

    Find the argument of :
    1 - cot (\frac{pi}{8})
    The answer is \frac{-3pi}{8}

    And i have no idea =(...doing cot(pi / 8) gives me some horrible decimal i can't work with...as does tan(pi/8)
    Any help would be really appreciated!
    Thank-you very much!
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  2. #2
    Super Member redsoxfan325's Avatar
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    You can find 1-cot(\frac{\pi}{8}) by using the half-angle identity: cot(\frac{x}{2}) = \frac{1+cos(x)}{sin(x)}, with x=\frac{\pi}{4}. This yields \frac{2+\sqrt{2}}{\sqrt{2}}. Subtracting from 1 and simplifying yields -\sqrt{2}. As for finding the argument, I'm not sure what you mean, as the argument is usually the angle something makes with the positive x-axis, and -\sqrt{2} is just a number, not a vector.
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  3. #3
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    uh is there a way to do this without the half angle identity because i havn't used that before?
    Thanks for reply
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  4. #4
    Super Member redsoxfan325's Avatar
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    Not that I know of, sorry.
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  5. #5
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    ok, thanks anyway =)
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