ab=12/5
[(ab+2)(2-ab)-4(ab-1)²]÷（-2ab）,
=[4-(ab)^2-4(ab)^2+8ab-4]÷（-2ab()
=[-5(ab)^2+8ab]÷（-2ab()
=1/2[5ab-8]
=1/2(5*12/5-8)=2是不是=-10哦对我ab= -12/5=1/2(-5*12/5-8)= -10