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1. I'm stuck on coverting 2x to 4x. I don't think we've even covered this topic.

Can anyone show a step by step to prove the following:

9(sin^2) 2x = 4.5(1 - cos 4x)

It will really help me... thanks !!!
2. (Original post by xskater)
I'm stuck on coverting 2x to 4x. I don't think we've even covered this topic.

Can anyone show a step by step to prove the following:

9(sin^2) 2x = 4.5(1 - cos 4x)

It will really help me... thanks !!!
well u have the identity that
cos 2u = cos^2 u - sin^2 u = (1 - sin^2 u) - sin^2u = 1 - 2sin^2 u

substituting u = 2x you get:
cos 4x = 1 - 2sin^2 2x
thus sin^2 2x = 1/2(1 - cos 4x)

and 9(sin^2) 2x = 4.5(1 - cos 4x)
3. Ohh cheers dude......

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