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Can someone please explain how my book got [itex] sin^{2} \theta = \frac{1-cos2\theta}{2} [/itex] and [itex] cos^{2}\theta = \frac{1+cos2\theta}{2} [/itex]

As I thought the half angle formula's were [itex] sin \frac{\theta}{2} = \sqrt{\frac{1-cos\theta}{2}} [/itex]

[itex] cos\frac{\theta}{2} = \sqrt\frac{1+cos\theta}{2}} [/itex]

So how can it also be the top one's aswell?

Thanks.

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# Homework Help: Half angle formula,

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