x-2xy-y分之2x-3xy-2y
=(2x-3xy-2y)/(x-2xy-y) 分子分母同时除以xy
=(2/y-3-2/x)/(1/y-2-1/x)
=[-3-2(1/x-1/y)]/[-2-(1/x-1/y)]
=(-3-6)/(-2-3)
=9/5