Three eccentricity formulas of ellipse: e=c/a(c stands for half focal length; A refers to the long half axis). Eccentricity =(ra-rp)/(ra+rp), where ra refers to the distance from the far point and rp refers to the distance from the near point. e=c/a=√[(a？ -B? )/a？ ]=√[ 1-(b/a)？ ]。

Eccentricity of ellipse: the unified definition of eccentricity is the ratio of the distance from the moving point to the focus and the distance from the moving point to the directrix. Eccentricity of an ellipse can be vividly understood as the degree to which two focal points leave the center on the premise that the long axis of the ellipse remains unchanged. Since it is a distance, there will be no negative number. The distance from any point on an ellipse to two focal points is equal to ex.