2/x-3/y=-1,即2y-3x+xy=0;
另x=2,y=3,则满足上式;
(9x-2xy-6y) / (-12+3xy-8y)
=(9*2-2*2*3-6*3) / (-12+3*2*3-8*3)
=-12/(-24)
=1/2