How is an ellipse different from a circle?
A circle is a closed curved shape that is flat. That is, it exists in two dimensions or on a plane. In a circle, all points on the circle are equally far from the center of the circle. An ellipse is also a closed curved shape that is flat. Instead of having all points the same distance from the center point, though, an ellipse is shaped so that when you add together the distances from two points inside the ellipse (called the foci) they always add up to the same number. Ellipses vary in shape from very broad and flat to almost circular, depending on how far away the foci are from each other. If the two foci are on the same spot, the ellipse is a circle.
