Animation 62

What geometric property is being dynamically illustrated in the applet below? [br][b][color=#0000ff]Note:[/color][/b] [color=#0000ff][i]The blue line is tangent to the conic section shown. [br][/i][/color]Feel free to move the [color=#000000]black point[/color], white point, and [color=#000000]black line[/color] anywhere you'd like!
Luk

Information: Animation 62