Question

$\cos(2x) \leqslant - \frac{1}{2}$

Поиогите​

Answer 1

$cos(2x)\leq -\frac{1}{2}\\\\\frac{2\pi}{3}+2\pi n\leq 2x\leq \frac{4\pi }{3}+2\pi n\; ,\; n\in Z\\\\\frac{\pi}{3}+\pi n\leq x\leq \frac{2\pi }{3}+\pi n\; ,\; n\in Z$