Double angle identities

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

$$\sin({2\alpha})=2\sin{\alpha}\cos{\alpha}$$ $$\cos({2\alpha})=\cos^2\alpha-\sin^2\alpha$$ $$\tan({2\alpha})=\frac{2\tan\alpha}{1-\tan^2\alpha}$$ $$\cot({2\alpha})=\frac{\cot^2\alpha-1}{2\cot\alpha}$$

2020-11-28