2cos (квадрат) 2x + cos2x + cos6x = 1

2cos²2x-1+cos2x+cos6x=0

cos2 (2x) + cos2x+cos6x=0

cos4x+cos2x+cos6x=0

cos4x+2*cos (6x+2x) / 2*cos (6x-2x) / 2=0

cos4x+2cos4x*cos2x=0

cos4x (1+2cos2x) = 0

cos4x=0

4x=π*n/2

x=π*n/8

1+2cos2x=0

2cos2x=-1

cos2x=-1/2

2x=2π/3+2πn

x=π/3+πn

2x=4π/3+2πn

x=2π/3+πn