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Math Help - trigonometry

  1. #1
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    trigonometry

    Solve equation sin(x + 15 ) = 3cos(x - 15) for 0 - 360 degrees.

    I started with

    sinx cos15 + cosx sin15 = 3( cosx cos15 + sinx sin15)

    i don't know where to go now

    thanks
    g
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  2. #2
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    Quote Originally Posted by gracey View Post
    Solve equation sin(x + 15 ) = 3cos(x - 15) for 0 - 360 degrees.

    I started with

    sinx cos15 + cosx sin15 = 3( cosx cos15 + sinx sin15)

    i don't know where to go now

    thanks
    g
    Put all the terms with \sin x on one side and all the terms with \cos x on the other. Then factor out \sin x and \cos x from their respective sides, so you get something like:

    \sin x(\cos 15 - 3\sin 15) = \cos x(3 \cos 15-\sin 15)

    Now assuming x \ne 90^o and x \ne 270^o, divide everything by \cos x, and you'll need to remember a very well known trig identity here to complete the final step.
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