tan(x-y)=(tanx-tany)/(1+tanx*tany)=[(sinxcosy-cosxsinx)/(cosxcosy) / [(cosxcosy+sinxsiny)/(cosxcosy)]=(sinxcosy-cosxsinx)/(cosxcosy+sinxsiny)=sin(x-y)/cos(x-y)(sinx+siny)²=0.25sin²x+sin²...