In this figure, the conic has one focus fixed at the origin. You can do two things to affect its shape:[br][list][*]Drag the directrix[/*][*]Change the eccentricity, [math]e[/math][br][/*][/list]The conic is then determined by the focus-directrix equation [math]PF=e\cdot PD[/math]. If [math]P[/math] is a point on the conic, then the distance from [math]P[/math] to the focus at the origin is [math]e[/math] times the distance from [math]P[/math] to the directrix.[br][br]All three types of conics -- ellipses, parabolas, and hyperbolas -- can be defined this way.[br]

[i]This applet was developed for use with [url=https://www.pearson.com/en-us/subject-catalog/p/interactive-calculus-early-transcendentals-single-variable/P200000009666]Interactive Calculus[/url], published by Pearson.[/i]