渐进线是y=2x,则双曲线是4x^2-y^2=k.(k不=0)
1.k>0: x^2/(k/4)-y^2/k=1
c^2=a^2+b^2=k/4+k=5k/4
e^2=c^2/a^2=(5k/4)/(k/4)=5
e=根号5
2.K