sinx-siny=1/3,cosx-cosy=2/3,sin(x+y)=?

sinx+siny=-1/3 cosx+cosy=1/2,求sin(x+y)的值. sinx+siny=1/2,cosx+cosy=（根号3）/3,求sin[(x-y)/2] 证明cosx(cosx-cosy)+sinx(sinx-siny)=2sin(x-y)/2 已知sinx+siny=1/3,cosx-cosy=1/5,求cos(x+y),sin(x-y). cosx+cosy=1/2,sinx-siny=1/3,则cos(x+y)=? 已知cosx+cosy=1/2,sinx-siny=1/3,求cos(x+y) 若cosx*cosy+sinx*siny=1/3 ,则cos(2x-2y)=? 已知sinx-siny=1/2,cosx-cosy=1/2,x、y均为锐角,求sin(x-y) sinx+siny=1/4,cosx+cosy=1/3求tan(x-y) cosx-cosy=4/1,sinx-siny=3/1求cos(x-y) 1、if sinx-siny= -1/3,cosx-cosy=1/2,then cos(x-y)=? 若sinx-siny=-1/3,cosx-cosy=1/2,则cos（x-y）=?