cos^2 - sin 2x= 0 ///////////////////
COS^2(X)-SIN(2X)=0
cos^2(x)-2sin(x)cos(x)=0
cos(x)[cos(x)-2sin(x)]=0
1) cos(x)=0
x=(pi/2)+pi*n
2) cos(x)-2sin(x)=0
cos(x)=2sin(x)
2sin(x)/cos(x)=cos(x)/cos(x)
2tg(x)=1
tg(x)=1/2
x=arctg(1/2)+pi*n