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Math Help - Trigonometric - Addition and subtraction Identities

  1. #1
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    Trigonometric - Addition and subtraction Identities

    sin(3x)cos(6x)-cos(3x)sin(6x)=-0.9
    I solve like this
    sin(3x)cos(6x)-cos(3x)sin(6x)=-0.9
    sin(3x-6x)=-0.9
    sin(-3x)=-0.9
    -sin(3x)=-0.9
    sin(3x)=0.9

    but the answer are 0.373+2π/3k and 0.6742π/3k
    π is pi.

    help please? am I doing the right way?
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  2. #2
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    Re: Trigonometric - Addition and subtraction Identities

    What you've done so far is fine, now you just have to evaluate the values of x...
    Thanks from edmundyong
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  3. #3
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    Re: Trigonometric - Addition and subtraction Identities

    got it! stupid me! I forget to change my answer to radian mode.
    thank you
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