Another Parabola Theorem!
In the applet below, a parabola is shown.
F = the focus of this parabola.
d = the directrix of this parabola.
V = the vertex of this parabola.
P = a point that lies ON the parabola.
(Feel free to move these points anywhere you'd like at any time.)
Note:
Segment t (that will soon appear) is tangent to the parabola at point P.
How can you formally prove what this applet informally illustrates?