решение:
4(1-cos(x)^2)+4cos(x)-1=0
4-cosx^2+4cosx-1=0
t=cosx
-4t^2+4t+3=0
t=3/2 и t=-1/2=>
cos(x)=3/2(x∉r) u cos(x)=-1/2
x=2pi/3+2pi*n
x=4pi/3+2pi*n
вроде так
