# Half angle identities

These half angle identities are very useful whenever expressions involving trigonometric functions need to be simplified.

$$\sin^{2}\frac{\alpha}{2}=\frac{1-\cos\alpha}{2}$$ $$\cos^{2}\frac{\alpha}{2}=\frac{1+\cos\alpha}{2}$$ $$\tan\frac{\alpha}{2}=\frac{\sin\alpha}{1+\cos\alpha}=\frac{1-\cos\alpha}{\sin\alpha}$$2020-11-28

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