Ellipse [distance/locus definition]

This example dynamically demonstrates the geometric definition of an ellipse as the locus of points where the sum of distances to two fixed points (foci) is constant. It involves core math concepts like ellipse definition, coordinate geometry, distance formula, and geometric construction. Key GeoGebra commands used are Circle and Intersect, with objects including foci F_1, F_2, constant r, center c, distance d, and points P_1, P_2. Suitable for high school mathematics to understand the geometric nature and construction of ellipses.