Ellipses from a distance-sum definition

Build understanding of ellipses from the constant sum of distances to two foci. This precalculus practice set connects standard equations with semiaxes, centers, vertices and focal positions in horizontal and vertical orientations. Problems include reconstruction, completing the square, geometric constraints and an elliptical arch model. Single-select and multiselect items include detailed worked solutions and checks of the conditions for a real, nondegenerate ellipse.