# Ellipse and its description

An ellipse is a closed plane curve, each point of which has a constant sum of distances from two fixed points, the so called foci E and F. The graph of the ellipse is in Fig. 1. The main parameters of the ellipse are the major axis, the minor axis and the linear eccentricity, see Fig. 1. It also introduces a numerical eccentricity ε = e/a, which is dimensionless in contrast to the linear eccentricity.

**Figure 1**Ellipse: vertices: A, B, co vertices: C, D, foci: E, F, major axis: a, minor axis: b, linear eccentricity e