Question

已知双曲线x2/4+y2/k=1的离心率为e>2,则实数k的取值范围是

Answer 1

x^2/4-y^2/(-k)=1

a^2=4 b^2=-k

c^2=a^+b^=4-k

e=c/a=(4-k)^0.5/2>2

(4-k)^0.5>4

4-k>16

k