丨3a+1丨+(2b-1)^2=0
则 3a+1=0 a=-1/3
2b-1=0 b=1/2
所以(3a^2 - 2b^2)/ab
=(3×1/9-2×1/4)/(-1/3)×1/2
=(-1/6)/(-1/6)
=1