Question

Решите неравенство: 2 cos 4x< -1

Answer 1

$2\, cos\, 4x<-1\\\\cos4x<-\frac{1}{2}\\\\\frac{2\pi}{3}+2\pi n<4x<\frac{4\pi}{3}+2\pi n\; ,\; n\in Z\\\\\frac{\pi}{6}+\pi n<x<\frac{\pi}{3}+\pi n\; ,\; n\in Z\\\\Otvet:\; \; x\in (\frac{\pi}{6}+\pi n\; ;\; \frac{\pi}{3}+\pi n\, )\; ,\; n\in Z$