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Math Help - Solve sin4(theta) = cos2(theta)

  1. #1
    dno
    dno is offline
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    Solve sin4(theta) = cos2(theta)

    dont worry about the values im just having trouble setting it up
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  2. #2
    Senior Member
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    Use the double angle identity \sin(4\theta)=2\sin(2\theta)\cos(2\theta).
    This gives:
    \sin(4\theta)=\cos(2\theta)
    2\sin(2\theta)\cos(2\theta)=\cos(2\theta)
    2\sin(2\theta)\cos(2\theta)-\cos(2\theta)=0
    \left(2\sin(2\theta)-1\right)\cos(2\theta)=0
    You should be able to see how to solve it from there.

    --Kevin C.
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