в) cos t = -$$\frac{1}{2}$$
t = ±arccos(-$$\frac{1}{2}$$) + 2$$\pi$$k, k ∈ Z
t = ±$$\frac{2\pi}{3}$$ + 2$$\pi$$k, k ∈ Z
Ответ: t = ±$$\frac{2\pi}{3}$$ + 2$$\pi$$k, k ∈ Z