1/a-1/b=3,所以a≠0,b≠0,所以ab≠0,
(-5a+4ab+5b)/(2a-3ab-2b) 分子分母同时除以ab
=(-5/b+4+5/a)/(2/b-3-2/a)
=[4+5(1/a-1/b)]/[-3-2(1/a-1/b)]
=(4+15)/(-3-6)
=-19/9