In the applet below, a parabola is shown. [br][br][b]F = the focus of this parabola.[br]d = the directrix of this parabola.[br]V = the vertex of this parabola. [/b][br][color=#9900ff][b]P = a point that lies ON the parabola. [/b][/color][br][br](Feel free to move these points anywhere you'd like at any time.) [br][br][color=#cc0000][b]Note:[/b][/color] [br][b]Segment [i]t[/i] (that will soon appear) is tangent to the parabola at[/b] [color=#9900ff][b]point [i]P[/i][/b][/color][b]. [/b] [br][br]How can you formally prove what this applet informally illustrates? [br]