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Math Help - Solving trigonometric equations:

  1. #1
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    Solving trigonometric equations:

    Solve for .

    Here's my work:
    sin(x) + sin(2x) = 0
    ___-
    what do I do now? I can't think of any trig identities or anything to simplify it? Do i just do sin(x) = - sin(2x) which obviously isn't true, does anyone know??
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  2. #2
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    Re: Solving trigonometric equations:

    Your pictures are broken. Try using Imageshack or some free image hosting. Or you can also upload to MHF, now that pictures appear to be working again.
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  3. #3
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    Re: Solving trigonometric equations:

    Sorry about that, the picture is solve for sin(x) + 2*sin(x)*cos(x) = 0 for 0 degrees <= x < 180 degrees
    I used a double angle idendtity to reduce from the aforementioned equation to sin(x) + sin(2x) = 0
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  4. #4
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    Re: Solving trigonometric equations:

    Quote Originally Posted by glambeth View Post
    Sorry about that, the picture is solve for \sin(x) + 2\sin(x)\cos(x) = 0 for 0 degrees <= x < 180 degrees
    Factor \sin(x)[1+2\cos(x)]=0 so
    \sin(x)=0~\text{ or }~\cos(x)=-\frac{1}{2}.
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  5. #5
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    Re: Solving trigonometric equations:

    I see now, so x is equal to 0, 120, or 180?
    Last edited by glambeth; August 12th 2011 at 10:07 AM.
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  6. #6
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    Re: Solving trigonometric equations:

    since x is strictly less than 180 degrees you should not take that as the answer.
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  7. #7
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    Re: Solving trigonometric equations:

    Thanks, no idea how I missed that!
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