3) $$cos (x+\frac{\pi}{3}) = 1$$

Решим уравнение $$cos (x+\frac{\pi}{3}) = 1$$. $$x+\frac{\pi}{3} = arccos(1) + 2\pi n, n \in Z$$ $$x+\frac{\pi}{3} = 0 + 2\pi n, n \in Z$$ $$x = -\frac{\pi}{3} + 2\pi n, n \in Z$$ Ответ: $$x = -\frac{\pi}{3} + 2\pi n, n \in Z$$