An [i]ellipse [/i]is a set of points in a plane whose distances from two fixed points (called [i]foci[/i]) have a constant sum. As you slide the slider, this definition is illustrated. The value of this constant sum is the length of the ellipse's major axis. You can drag[color=#ff00ff] [b]point [i]P[/i][/b] [/color]anywhere on this ellipse to see the illustration.[br][br]The equation of an ellipse centered at the origin with foci [math]F_1[/math] and [math]F_2[/math] is given in this interactive figure. Its [color=#1e84cc][b]semimajor axis[/b][/color], and its [b][color=#b4a7d6]semiminor axis[/color][/b] and[color=#ff7700] distance, [i]c[/i], from the ellipse's center to any one of its foci [/color]are also displayed here. You can adjust the graph of the ellipse by moving the larger [b]black points[/b].

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