Question

cos2x$geq$-1/корень из 2

Answer 1

$cos(2x) geq -frac{1}{sqrt{2}}$
$frac{-3*pi}{4}+2*pi*k<2x<frac{3*pi}{4}+2*pi*k$
$-frac{3*pi}{8}+pi*k<x<frac{3*pi}{8}+pi*k$
x є $-frac{3*pi}{8}+pi*k;frac{3*pi}{8}+pi*k$
k є Z