2 cos^2 x - 3 cos x +1 = 0
сosx=y
2y²-3y+1=0
D=(-3)²-4*1*2 = 9-8=1
y1=(3+1)/4=1
y2=(3-1)/4=1/2=0.5
cosx = 1
x=2pi n, n є Z
cosx=1/2
x=±pi/3 + 2pi n, n єZ
