解
a²-4a+b²+2b+5=0
(a²-4a+4)+(b²+2b+1)=0
(a-2)²+(b+1)²=0
∴a-2=0,b+1=0
∴a=2,b=-1
∴(2a+b)/(2a-b)
=(4-1)/(4+1)
=3/5