(k+2)^2-4*1*(1/4k^2+1)>0
k>0时有两不等实根;
x1+x2=k+2
x1*x2=1/4k^2+1
(x1+x2)^2-4*(x1x2)=(x1-x2)^2
x1-x2=正负2倍根号k;
x2〉0;k+2=4,k=2,x1=2-2倍根号2,x2=2倍根号2
x2〈0;2倍根号k=4,k=4,x1=5,x2=1
-2倍根号k=4,不可能;