ЛК
Людмила Кузьмичёва
cos(2x) = 2cos(x) - 1
cos^2(x) - cos(x) = 0
cos(x) = 1 --> x = 2πk
cos(x) = 0 --> x = π/2 + πk
k - целое.
2 cos^2(x)- 1 - 2 cos x+1 = 0
cos^2(x) - cos x =0
cos x (cos x -1) =0
cos x =0 x = П/2 + Пп
cos x -1 = 0 х =2Пп