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Math Help - sin(4x)*cos(x) = 0.84

  1. #1
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    sin(4x)*cos(x) = 0.84

    I am having a hard time with this problem. The only thing I can think to do is change cos(x) to (1-sin^2(x)) but im not even sure how that would help. What step am I missing here?
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  2. #2
    Junior Member toraj58's Avatar
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    \color{blue}\boxed{\sin(4x) = 2\sin(2x)\cos(2x)}

    and

    \sin(2x) = 2\sin(x)\cos(x)

    and

    \cos(2x) = \cos^2 (x) - \sin^2 (x)

    also please notice that cos(x) is not equal to 1-sin^2x

    but

    \cos^2 (x) = 1 - \sin^2 (x)
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  3. #3
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    Thank you. However, I am still having problems.

    Sin(4x) * Cos(x) = 0.84
    2*Sin(2x)*cos(2x) * cos(x) =0.84
    2*2*Sin(x)*cos(x)*(cos^2x-sin^2x)*cos(x) = 0.84
    4*sin(x)*cos^2(x)*(cos^2x-sin^2x) = 0.84
    sin(x)*cos^2(x)*(cos^2x-sin^2x)=0.21

    Forgive me, but I am not sure how to further simplify this problem.
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