What is foci definition?

Foci are defined as the two points on the major axis of an ellipse (or hyperbola), which are equidistant from the center. The distance between the center and each focus is denoted by the letter c and is a constant value regardless of the shape or size of the ellipse. The foci play an important role in the properties and behavior of ellipses, such as reflecting sound waves or light rays. They can also be used to determine the shape and size of the ellipse based on their distance from each other and the length of the major and minor axes. The foci of a hyperbola also play an important role in the shape and behavior of the conic section.