Помогите с решение заданий 3 задания хороший бал тема тригонометрия

$1. ctg240=ctg(180+60)=ctg60=\frac{cos60}{sin60}=\frac{\sqrt3/2}{1/2}=\sqrt3\\ cos\frac{5\pi}{3}=cos(\pi+\frac{2\pi}{3})=-cos\frac{2\pi}{3}=-0.5$

2. $\frac{sin(\pi+\alpha)*sin(\alpha+2\pi)}{tg(\pi+\alpha)*cos(1.5\pi+\alpha)}=\frac{-sin \alpha*sin \alpha}{tg\alpha*cos(\frac{3\pi}{2}+\alpha)}=\frac{-sin^2 \alpha}{\frac{sin\alpha}{cos\alpha}*(-sin\alpha)}=cos\alpha$

3. $ctg\frac{7\pi}{3}=ctg(2\pi+\frac{\pi}{3})=ctg\frac{\pi}{3}=\frac{cos\frac{\pi}{3}}{sin\frac{\pi}{3}}=\frac{1/2}{\sqrt3/2}=\frac{1}{\sqrt3}$