A与B互为相反数
A=-B
A减B的绝对值 等于5分之4
|A-B|=4/5
|-B-B|=|2B|=4/5
2B=±4/5
B=±2/5
A=2/5,B=-2/5或A=-2/5,B=2/5
所以 AB=-2/5*2/5=-4/25
(A-AB+B)/(A^2+AB+1)
=[(A+B)-AB]/[A(A+B)+1]
=[0-(-4/25)]/(A*0+1)
=4/25