Cos x-cos 3x + sin x=0

cos x - cos 3x + sin x = 0;
2sin 2x sin x + sin x = 0;
sin x(2sin 2x + 1) = 0;
sin x = 0;
x = пn, n∈Z;
2sin 2x + 1 = 0;
sin 2x = - 1/2;
2x = + arcsin(-1/2);
2x = 2пk - arcsin(-1/2);
2x = 2пk - п/6; k∈Z;
2x = 2пk + 7п/6; k∈Z;
x1 = пk - п/12; k∈Z;
x2 = пk + 7п/12; k∈Z;
Ответ: x = пn, n∈Z; x1 = пk - п/12; k∈Z; x2 = пk + 7п/12; k∈Z;