Recall that an ellipse is a locus (set) of points in the plane for which the [b][color=#0000ff]sum[/color][/b] of the distances from two fixed points, called foci, remains constant.  [br][br]In the applet below, feel free to adjust the [color=#000000][b]black siders[/b][/color] and the location of the [color=#980000][b]brown point (x,y)[/b][/color] on the ellipse before dragging the blue slider.  [br][br]What is the value of this [color=#0000ff][b]special sum[/b][/color]?