Algebra/Chapter 17/Ellipses

Algebra Ellipse Circle Hyperbola right right An ellipse is the collection of points that are equidistant from two points, called foci (singular focus). The foci are found on the major axis, which has a length of 2a. The minor axis is 2b, and is smaller. The "roundness" or "longness" of an ellipse can be measured by eccentricity. If c is the distance from the center to a focus, then e = c / a. The latus rectum is a line parallel to the minor axis that crosses through a focus. Its length is b2 / a. "Long" ellipses are generally written as where (h,k) is the center, while "tall" ellipses are written as thumb|none|A method to locate the foci of any ellipse: the foci (purple crosses) are at intersects of the major axis (red) and a circle (cyan) of radius equal to the semi-major axis (blue), centred on an end of the minor axis (grey)