A [i]parabola [/i]can be defined as the set of points in a plane that are equidistant from a given point (the focus) and a fixed line (the directrix). Drag the [b]black slider[/b] to illustrate this definition. You can move [color=#1e84cc][b]point [i]P[/i][/b][/color] anywhere you'd like prior to doing so. [br][br]In this figure, [i]p[/i] = the directed distance from the vertex [math]V[/math], to the focus [math]F[/math]. [color=#0000ff]When [i]p[/i] > 0 the focus and directrix are displayed in blue[/color]. [color=#cc0000]When [i]p[/i] < 0, these elements become red[/color]. [br][br]

[i]Developed for use with Thomas' Calculus, published by Pearson.[/i]