1、cosx-cosy=1/2 ,sinx-siny=-1/3分别两边平方(cosx)^2-2cosxcosy+(cosy)^2=1/4(sinx)^2-2sinxsiny+(siny)^2=1/9相加且(cosx)^2+(sinx)^2=1 (cosy)^2+(siny)^2=12-2(cosxcosy+sinxsiny)=1/4+1/9=13/36cos(x-y)=cosx...