a^2-4a+b^2-b/2+65/16=0
a^2-4a+4 +b^2-b/2+1/16=0
(a-2)^2+(b-1/4)^2=0
a-2=0 b-1/4=0
a=2 b=1/4
a的平方-4根号b
=2^2-4√1/4
=4-4*1/2
=4-2
=2