1) $$cosx = - \frac{\sqrt{2}}{2}$$

Решим уравнение $$cosx = - \frac{\sqrt{2}}{2}$$. $$x = \pm arccos(-\frac{\sqrt{2}}{2}) + 2\pi n, n \in Z$$ $$x = \pm \frac{3\pi}{4} + 2\pi n, n \in Z$$ Ответ: $$x = \pm \frac{3\pi}{4} + 2\pi n, n \in Z$$