c^2/a^2+4c^2/(a^2-c^2)=1,
e=c/a,
e^2+4e^2/(1-e^2)=1,
令t=e^2,
t+4t/(1-t)=1,
t^2-6t+1=0,
t=3±2√2,∵3+2√2》1,应舍去,
t=3-2√2,
e=√（3-2√2）=√（2-2√2+1）=√（√2-1）^2=√2-1.