4x^2+y^2-4x+10y+26=0
4x^2-4x+1+y^2+10y+25=0
(2x-1）^2+(y+5)^2=0
非负数之和为零,所以两个非负数都为零
2x-1=0,y+5=0
x=1/2,y=-5
12x-y=6-（-5）=11
12x-y的平方根=正负根号11