б) cos t = -$$\frac{\sqrt{3}}{2}$$
t = ±arccos(-$$\frac{\sqrt{3}}{2}$$) + 2$$\pi$$k, k ∈ Z
t = ±$$\frac{5\pi}{6}$$ + 2$$\pi$$k, k ∈ Z
Ответ: t = ±$$\frac{5\pi}{6}$$ + 2$$\pi$$k, k ∈ Z