a^2-4a+b^2-2b+5=0a^2-4a+4+b^2-2b+1=0(a-2)^2+(b-1)^2=0a=2 b=1a^2+ab/（a+b)^2=2^2+2*1/(2+1)^2=2/3
a^2-4a+b^2-2b+5=0则(a-2)^2 -4 + (b-1)^2 - 1 + 5 =0(a-2)^2 + (b-1)^2 =0则a=2 b=1代入原式可得答案为4+2/9
