б) cos t = $$\frac{\sqrt{2}}{2}$$
t = ±arccos $$\frac{\sqrt{2}}{2}$$ + 2$$\pi$$k, k ∈ Z
t = ±$$\frac{\pi}{4}$$ + 2$$\pi$$k, k ∈ Z
Ответ: t = ±$$\frac{\pi}{4}$$ + 2$$\pi$$k, k ∈ Z