sin（x+y）=sinxcosy+cosxsiny=1/2,sin（x-y）=sinxcosy-cosxsiny=1/3,两式作商得(sinxcosy+cosxsiny)/(sinxcosy-cosxsiny)=3/2,分子分母同时除以cosxcosy得(tanx+tany)/(tanx-tany)=3/2,所以2tanx+2tany=3tanx-3tan...