 Ellipse

An ellipse is the locus of points whose distances from two fixed foci have constant sum. If the focal distance is $d$ and the sum is $c>d$, its semimajor and semiminor axes are $c/2$ and $\sqrt{c^2-d^2}/2$.

An ellipse is a shape that can be defined in several ways in mathematics and geometry. Here are some key points about ellipses: 1. **Geometric Definition**: An ellipse is the set of all points in a plane where the sum of the distances from two fixed points (called foci) is constant. This characteristic gives rise to its elongated circular shape.