Решите уравнение cos2x+10cosx-11=0. помогите ПОЖАЛУЙСТА))))

cos2x + 10cosx - 11 = 0cos^2 x - sin^2 x + 10 cosx - 11 = 0cos^2 x - (1 - cos^2 x) + 10 cosx - 11 = 02cos^2 x + 10 cosx - 12 = 0, cos x = t2t^2 + 10t - 12 = 0t^2 + 5t - 6 = 0D = 5^2 + 4*6 = 25 + 24 = 49t1 = (-5 + 7)/2 = 2/2 = 1t1 = (-5-7)/2 = -12/2 = -6 - лишний кореньcos x = 1x = pin, n э Z