Other curves: conics
The ellipse,
This display illustrates a property of all ellipses. Any ellipse has two points called the foci - points F1 and F2 in the diagram. Any point, P, on the ellipse has the property that the sum of its distances from F1 and F2 is always the same. Move point P to see this. You can change the constant, s, too by using the buttons .

Conic curves The ellipse is an example of a conic curve. This means that you can make a slice (shown in green) through a cone that creates a elliptic cross-section (shown in red).