The slope of the straight line is 2/2 of the root sign, that is, the inclination angle is 45 degrees.
So the abscissa and ordinate of the intersection point are equal, that is, x = y = c;;
B = a-c, substitute into ellipse:
c^/a^+c^/(a^-c^)= 1,
E=c/a substitution, simplified as:
e^4-3e^2+ 1=0,
Because 0
e^=(3-√5)/2,
Prescription, e=(√5- 1)/2.