Definition of a Parabola
Line AB is the directrix for the Parabola below.
Point C is the focus of the Parabola below.
Point D lies on the Parabola below.
d1 is the distance from the focus to point D.
d2 is the distance from the directrix to point D.
Move points A or B to change the directrix. Move point C to change the location of the focus.
Then move point D around the Parabola.