若a/b=2,求(a²+ab-b²)/(a²-2ab+2b²)的值

问题描述:

若a/b=2,求(a²+ab-b²)/(a²-2ab+2b²)的值

a/b=2
将a=2b代入
(a²+ab-b²)/(a²-2ab+2b²)
=(4b²+2b²-b²)/(4b²-4b²+2b²)
=5/2