有这样的一种椭圆，它的长半轴、短半轴、半焦距分别是如图1所示的直角三角形ABC的斜边BC及直角边CA、BA的长a、b、C，且BA边在斜边BC上的射影BH的长恰等于CA边的长b，即是说，D是线段BC的黄金分割点．这时，由CA~2=DC·BC得定义如果椭圆的短半轴和长半轴的长之比等于，那么就 There is an ellipse whose major axis, short axis, and half focal lengths are the hypotenuse BC of the right angled triangle ABC and the longa, b, and C of the right angled edges CA and BA shown in FIG. 1, respectively. The length of the projective BH on the hypotenuse BC is exactly equal to the length b of the CA side, that is, D is the golden section of the segment BC. At this time, it is defined by CA~2=DC•BC if the ratio of the lengths of the short semiaxis and the long semiaxis of the ellipse is equal to