Definition of an Ellipse

This example demonstrates the definition of an ellipse as the set of all points where the distance to a fixed point (focus) is a constant ratio (eccentricity) to the distance to a fixed line (directrix). Key mathematical concepts include focus, directrix, eccentricity, coordinate geometry, and geometric construction. Construction involves commands like Point, Mirror, Ellipse, Segment, Intersect, Circle, and LaTeX, utilizing objects such as C, A, A', c, B, a, b, D, g, l, text1, d, m, text2. Suitable for high school students learning about ellipses and their properties.