sinX-xinY=-2/3 , cosX-cosY=2/3 ,且X,Y都为锐角。

(sinx-siny)^2=(sinx)^2+(siny)^2-2sinxsiny=4/9
(cosx-cosy)^2=(cisx)^2-2cosxcosy+(cosy)^2=4/9
所以2-2(sinxsiny+cosxcosy)=8/9
cos(x-y)=5/9

sinx-siny<0,x,y都为锐角
所以x<y
且-90度<x-y<0
所以sin(x-y)<0
[cos(x-y)]^2+[sin(x-y)]^2=1
所以sin(x-y)=-2√14/9
所以tan(x-y)=(-2√14/9)/(5/9)=-2√14/5