Question

cos^2(3x)-sin^2(3x) > -0.5

Answer 1

$cos^23x-sin^23x textgreater -0.5\ \ cos6x textgreater -0.5\ \ - frac{2 pi }{3} +2 pi n textless 6x textless frac{2 pi }{3} +2 pi n\ \ - frac{pi}{9} + frac{pi n}{3} textless x textless frac{pi}{9}+ frac{pi n}{3},n in mathbb{Z}$