A point related to the construction and properties of conic sections. Hyperbolas and noncircular ellipses have two distinct foci and two associated conic section directrices, each directrix being perpendicular to the line joining the two foci (Eves 1965, p. 275).
Focus
See also
Conic Section Directrix, Eccentricity, Ellipse, Ellipsoid, Focal Parameter, Hyperbola, Hyperboloid, Parabola, Paraboloid, Reflection PropertyExplore with Wolfram|Alpha
References
Coxeter, H. S. M. and Greitzer, S. L. Geometry Revisited. Washington, DC: Math. Assoc. Amer., pp. 141-144, 1967.Eves, H. "The Focus-Directrix Property." §6.8 in A Survey of Geometry, rev. ed. Boston, MA: Allyn & Bacon, pp. 272-275, 1965.Referenced on Wolfram|Alpha
FocusCite this as:
Weisstein, Eric W. "Focus." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Focus.html