a分之1 减 b分之1 = 3,求分式（a-ab-b）分之（2a+3ab-2b）的值.
问题描述：
a分之1 减 b分之1 = 3,求分式（a-ab-b）分之（2a+3ab-2b）的值.
答
∵ 1/a-1/b=3
∴ b-a=3ab
a-ab-b=a-b-ab
=-3ab-ab
=-4ab
2a+3ab-2b=2(a-b)+3ab
=2×(-3ab)+3ab
=-3ab
∴原式=-4ab/(-3ab)
= 4/3