Question

双曲线,实轴、虚轴、焦距为等差数列

Answer 1

2*2b=(2a+2c)

2b=a+c

b=(a+c)/2

b^2+a^2=c^2

a^2+2ac+c^2+4a^2=4c^2

3c^2-2ac-5a^2=0

(c+a)(3c-5a)=0

c+a>0

所以3c=5a

e=c/a=5/3