# Thread: Solve sin4(theta) = cos2(theta)

1. ## Solve sin4(theta) = cos2(theta)

dont worry about the values im just having trouble setting it up

2. 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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# cos 2 theta ÷ sin 4 theta = 1

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