sin(x+y)=sinx*siny+cosx*cosy
cos(x+y)=sinx*cosy-cosy*siny
tan(x+y)=(1+tanx*tany)/(tanx-tany)
sin(x-y)=sinx*siny-cosx*cosy
cos(x-y)=sinx*cosy+cosy*siny
tan(x+y)=(tanx*tany-1)/(tanx+tany)
sin(x+y)=sinx*siny+cosx*cosy
cos(x+y)=sinx*cosy-cosy*siny
tan(x+y)=(1+tanx*tany)/(tanx-tany)
sin(x-y)=sinx*siny-cosx*cosy
cos(x-y)=sinx*cosy+cosy*siny
tan(x+y)=(tanx*tany-1)/(tanx+tany)