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Thread: trigonometry help pls

  1. September 16th 2008, 11:33 AM #1
    snowball
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    Talking trigonometry help pls

    1) cos(x-30)=3cos(x+30) find x for 0<x<360 degrees

    2) 4tan2xtanx=1 find x for 0<x<2pi in radians

    thanks
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  2. September 16th 2008, 11:41 AM #2
    icemanfan
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    For the first problem, use the angle sum identities for cosine. \cos (x - 30) = \cos x \cos 30 + \sin x \sin 30 and \cos (x + 30) = \cos x \cos 30 - \sin x \sin 30. You should be able to simplify the original equation to 4 \sin x \sin 30 = 2 \cos x \cos 30 and work it from there.
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  3. September 16th 2008, 11:51 AM #3
    snowball
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    why didn't i thought of that... i'm so stupid... thanks...


    I just figured out question 2, thanks again icemanfan
    Last edited by snowball; September 16th 2008 at 01:08 PM.
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