已知1/a - 1/b=4,则(a-2ab-b)/(2a-2b+7ab)的值等于A.6 B.-6 C.2/15 D.-2/7

已知1/a - 1/b=4,则(a-2ab-b)/(2a-2b+7ab)的值等于A.6 B.-6 C.2/15 D.-2/7
已知1/a - 1/b=4,则(a-2ab-b)/(2a-2b+7ab)的值等于
A.6 B.-6 C.2/15 D.-2/7

已知1/a - 1/b=4,则(a-2ab-b)/(2a-2b+7ab)的值等于A.6 B.-6 C.2/15 D.-2/7
1/a - 1/b=4
(b-a)/ab=4
b-a=4ab
(a-2ab-b)/(2a-2b+7ab)=
-(b-a+2ab)/-(2(b-a)-7ab)=
(4ab+2ab)/(8ab-7ab)=
6ab/ab=6
OK