Δ=（2k+1）^2-4(k^2+1)=4k-3≥0
k≥3/4
x1/x2=1/2 x2=2x1
x1+x2=2k+1=3x1
x1*x2=2x1^2=k^2+1
以x1^2为等量建立方程
k^2-8k+7=0
(k-7)(k-1)=0
k=7ork=1