Вычислите: а)arccos$\left[\vphantom{\sin\left(-\frac{\pi}{7}\right)}\right.$sin$\left(\vphantom{-\frac{\pi}{7}}\right.$-${\frac{\pi}{7}}$$\left.\vphantom{-\frac{\pi}{7}}\right)$$\left.\vphantom{\sin\left(-\frac{\pi}{7}\right)}\right]$; б)arcsin$\left(\vphantom{\cos\frac{33\pi}{5}}\right.$cos${\frac{33\pi}{5}}$$\left.\vphantom{\cos\frac{33\pi}{5}}\right)$.