Cos 6x = 1 - 2sin^2(3x)
cos(3pi/2 - 3x) = -sin(3x)
Подставляем
1 - 2sin^2(3x) - √2*sin(3x) = 1
-2sin^2(3x) - √2*sin(3x) = -√2*sin(3x)*(√2*sin(3x) + 1) = 0
1) sin(3x) = 0
3x = pi*k
x1 = pi/3*k
2) sin(3x) = -1/√2;
3x = -pi/4 + 2pi*k; x2 = -pi/12 + 2pi/3*k
3x = 5pi/4 + 2pi*k; x3 = 5pi/12 + 2pi/3*k