a) arccos(-0.5) + arcsin(-0.5) = $$\frac{2\pi}{3} + (-\frac{\pi}{6})$$ = $$\frac{4\pi - \pi}{6}$$ = $$\frac{3\pi}{6}$$ = $$\frac{\pi}{2}$$.
Ответ: $$\frac{\pi}{2}$$