a²＋b²＋5／4＝2a－b
a²-2a+1+b²+b+1/4=0
(a-1)²+(b+1/2)²=0
a-1=0,b+1/2=0
a=1,b=-1/2
ab/a+b=-1/2÷(1-1/2)=-1