# Trigonometry Homework #11 due 5-18

Prove each identity.

1. $\cos^4\theta-\sin^4\theta=\cos(2\theta)$
2. $\sin(4x)=4\sin{x}\cos{x}\cos(2x)$
3. $\frac{\sin(2x)}{1+\cos(2x)}=\tan{x}$
4. $\cot\alpha+\tan\alpha=2\csc(2\alpha)$
5. $\tan(\pi-\alpha)=-\tan{\alpha}$