It is a problem that is only studied in the quadratic definition of ellipse, and it rarely appears in general big problems.
His geometric meaning can refer to the directrix of parabola. Parabolas are equal and ellipses are proportional.
That is to say, the distance from any point on the ellipse to the focal point on the same side is proportional to the distance to the corresponding directrix, and this ratio is the geometric meaning of eccentricity.
O is the origin of the coordinate system. F is the point. The module length of is C.
In the figure, l 1, l2 is the alignment.