y=3xy+x ->xy=(y-x)/3
2x+3xy-2y=2x+y-x-2y=x-y
x-2xy-y=x-(2/3)(y-x)-y=(5/3)(x-y)
2x+3xy-2y除以x-2xy-y =(x-y)/(5/3)(x-y)=3/5