a^2b^2+a^2+b^2+1=4ab
(ab-1)^2+(a-b)^2=0
由非负数性质得
(ab-1)^2=0,(a-b)^2=0
ab=1,a^2+b^2-2ab=0
a^2+b^2=2ab=2*1=2
a^2+b^2=2