sin²x/2+2sinx/2-sinx-4cosx/2=0
sin(x/2)[sin(x/2)+2]-2sin(x/2)cos(x/2)-4cos(x/2)=0
sin(x/2)[sin(x/2)+2]-2cos(x/2)[sin(x/2)+2]=0
提取公因式,即得：
[sin(x/2)-2cos(x/2)]*[sin(x/2)+2]=0