Вычислите: а) sin 9п/4= б) cos ( -4п/3)= в) tg (-7п/6) = г) ctg 5п/4

Решите задачу:

$\sin (\frac{9 \pi}{4})=\sin (2 \pi +\frac{ \pi}{4})=\sin (\frac{\pi}{4})=\frac{\sqrt{2}}{2} \\ \\ \cos (-\frac{4 \pi}{3})=\cos (\frac{4\pi}{3})=\cos (\pi + \frac{\pi}{3})=-\cos (\frac{\pi}{3})=- \frac{1}{2} \\ \\ tg(-\frac{7\pi}{6})=-tg(\frac{7\pi}{6})= - tg (\pi + \frac{\pi}{6})=-tg (\frac{\pi}{6})=-\frac{\sqrt{3}}{3} \\ \\ ctg(\frac{5 \pi}{4})=ctg (\pi+\frac{\pi}{4})=ctg (\frac{\pi}{4})=1$