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Math Help - Trig inequality.

  1. #1
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    Trig inequality.

    I'm trying to show that

    5+8cos\theta+4cos2\theta+cos3\theta\geq0

    but keep going around in circles.

    Can anybody take a stab at it?
    Last edited by mr fantastic; April 20th 2011 at 05:05 AM. Reason: Title.
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  2. #2
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    Uhm, what don't you know? Also, what have you tried and didn't work?

    Try to use and .
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  3. #3
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    Quote Originally Posted by Cairo View Post
    I'm trying to show that

    5+8cos\theta+4cos2\theta+cos3\theta\geq0

    but keep going around in circles.

    Can anybody take a stab at it?
    A start would probably be to express and in terms of .
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