1/a-1/b=1
b-a=ab
(2a+3ab-2b)/(a-2ab-b)
=(2a+3b-3a-2b)/(a+2a-2b-b)
=(b-a)/3(a-b)
=-1/3
1/a-1/b=3
b-a=3ab
(2a+3ab-2b)/(a-2ab-b)
=(3ab-6ab)/(-3ab-2ab)
=-3ab/(-5ab)
=3/5