3a²+ab-2b²=0
两边同除以a²得
3+b/a-2(b/a)²=0
解得b/a=-1或b/a=3/2
a/b-b/a-(a²+b²)/(ab)
=(a²-b²)/(ab)-(a²+b²)/(ab)
=-2b/a
=2或-3