A curve whose name means ``shell form.'' Let be a curve and a fixed point. Let and be points on a line from to meeting it at , where , with a given constant. For example, if is a Circle and is on , then the conchoid is a Limaçon, while in the special case that is the Diameter of , then the conchoid is a Cardioid. The equation for a parametrically represented curve with is
See also Concho-Spiral, Conchoid of de Sluze, Conchoid of Nicomedes, Conical Spiral, Dürer's Conchoid
References
Lawrence, J. D. A Catalog of Special Plane Curves. New York: Dover, pp. 49-51, 1972.
Lee, X. ``Conchoid.''
http://www.best.com/~xah/SpecialPlaneCurves_dir/Conchoid_dir/conchoid.html.
Lockwood, E. H. ``Conchoids.'' Ch. 14 in A Book of Curves. Cambridge, England: Cambridge University Press,
pp. 126-129, 1967.
Yates, R. C. ``Conchoid.'' A Handbook on Curves and Their Properties. Ann Arbor, MI: J. W. Edwards, pp. 31-33, 1952.