Question

Решите неравенства Cos ($\frac{x}{3}$)$\leq$$\frac{\sqrt{2} }{2}$

Answer 1

$\cos \dfrac{x}{3}\leq \dfrac{\sqrt{2}}{2}\\ \\ \dfrac{\pi}{4}+2\pi n\leq \dfrac{x}{3}\leq \dfrac{7\pi}{4}+2\pi n,n \in \mathbb{Z}\\ \\ \boxed{\dfrac{3\pi}{4}+6\pi n\leq x\leq \dfrac{21\pi}{4}+6\pi n,n \in \mathbb{Z}}$