2sinx=1+cosx
sinx=(1+cosx)/2
sinx=[cos(x/2)]^2
2sin(x/2)cos(x/2)=[cos(x/2)]^2
[2sin(x/2)cos(x/2)]/[cos(x/2)]^2=1
2[sin(x/2)/cos(x/2)]=1
tan(x/2)=1/2