Question

Помогите решить уравнение 2 cos2 x-cos x-1=0

Answer 1

$2 { cos(x) }^{2} - cos(x) - 1 = 0 \ cos(x) = t \ - 1 leqslant t leqslant 1 \ 2 {t}^{2} - t - 1 = 0 \ t(1) = 1 \ t(2) = - frac{1}{2} \ cos(x) = 1 \ x = 2pi n \ cos(x) = - frac{1}{2} \ x = frac{2pi}{3} + 2pi k \ x = frac{4pi}{3} + 2pi m$