1/a-1/b=3
b/ab-a/ab=3
b-a=3ab
(2a-3ab-2b)/(a-2ab-b)=-(2b-2a+3ab)/-(b-a+2ab)=[2(b-a)+3ab]/b-a+2ab=(6ab+3ab)/(3ab+2ab)=9ab/5ab
因为1/a+1/b=3
所以a,b不等于0
所以9ab/5ab=1.8