Reflexion and the gardeners rule

We mark two neighbour points A and B on the ellipse and the two pairs of rays from the focal points to obtain C and D. The perpendiculars from A mark G and H. The gardeners rule yields CB = BH. Then, the triangles AGB and AHB are congruent (up to reflexion) and the angles ABG and ABH are equal.

Kapitel und Portal
  gardeners rule: reflexion at the ellipse: