- #1

tweety1234

- 112

- 0

## Homework Statement

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.