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Thread: Solving a trig equation

  1. Jul 21st 2009, 08:04 AM #1
    mp3qz
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    Solving a trig equation

    Please solve

    3./ cos3x - sin 3x + 2cosx = 0
    Last edited by mr fantastic; Jul 21st 2009 at 05:56 PM. Reason: Moved question to new thread and edited accordingly
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  2. Jul 22nd 2009, 02:22 PM #2
    pickslides
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    Quote Originally Posted by mp3qz View Post
    Please solve

    3./ cos3x - sin 3x + 2cosx = 0
    Maybe you could consider

    \sin(3x) = 3 \sin(x)-4\sin^3(x)

    and

    \cos(3x) = 4\cos^3(x)- 3 \cos(x)
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  3. Jul 23rd 2009, 08:13 AM #3
    red_dog
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    Quote Originally Posted by pickslides View Post
    Maybe you could consider

    \sin(3x) = 3 \sin(x)-4\sin^3(x)

    and

    \cos(3x) = 4\cos^3(x)- 3 \cos(x)
    Using the hint of pickslides the equation becomes

    4\sin^3x+4\cos^3x-3\sin x-\cos x=0

    which is the same equation like in this thread: http://www.mathhelpforum.com/math-he...-equation.html
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