Ellipse Construction and the "String Property"
- Nathan Smith
An ellipse is the set of all points in a plane such that the sum of the distances of those points from two fixed points (called the foci) is constant. In the diagram below, d1 + d2 is constant, and those two distances are the radii of the circles you see. The points of intersection of the those two circles created share a total distance of d1 + d2 from the foci. The points traced out form an ellipse.