2cos2x-2cos4x+2cos2x+1=0
4cos2x-2cos4x+1=0
4cos2x-2(2cos^22x-1)+1=0
4cos2x-4cos^22x+3=0
cos2x=t
4t^2-4t-3=0
t=(2+-4)/4
|t|<=1
t=-1/2
cos2x=-1/2
2x=2Пk+-2П/3
x=Пk+-П/3
k=1 x=П-П/3=2/3П
k=0 x=П/3
ответ х=П/3
