cos2x=2cos^2x-1
2cos^x+cosx-1=0
cosx=y
2y^2+y-1=0
D=1+8=9
y1=-1+3/4=1
y2=-1/2
cosx=1
x=2pin n€Z
cosx=-1/2
x=+-pi/3+2pin n€Z
cos2x=2cos^2x-1
2cos^x+cosx-1=0
cosx=y
2y^2+y-1=0
D=1+8=9
y1=-1+3/4=1
y2=-1/2
cosx=1
x=2pin n€Z
cosx=-1/2
x=+-pi/3+2pin n€Z