- Kai-Yong Lin
Introduction to Parabola: definition and properties --------- 1. Try to drag P to see if the Distance[P,F] is always equal to Distance[P,directrix]. (Hint: Any point P on the parabola is equidistant from the directrix and the focus.) 2.Drag the focus F close to / far away from the directrix to see what the curve varies. (Hint: What happens while focal length c varies?) 3.Set the directrix to be horizontal or vertical line, then determine the parabola equation in standard form by yourself.
What will happen if the focus F lies on the directrix?