Question

cos2x<-0,5 решите неравенство

Answer 1

$cos2x\ \textless \ -0,5\\\\\frac{2\pi}{3}+2\pi n\ \textless \ 2x\ \textless \ \frac{4\pi}{3}+2\pi n,\; n\in Z\\\\\frac{\pi}{3}+\pi n\ \textless \ x\ \textless \ \frac{2\pi}{3}+\pi n,\; n\in Z$