The curve described by a point at a distance from the center of a rolling Circle of Radius .
See also Curtate Cycloid, Cycloid, Prolate Cycloid
References
Lee, X. ``Trochoid.''
http://www.best.com/~xah/SpecialPlaneCurves_dir/Trochoid_dir/trochoid.html.
Wagon, S. Mathematica in Action. New York: W. H. Freeman, pp. 46-50, 1991.
Yates, R. C. ``Trochoids.'' A Handbook on Curves and Their Properties. Ann Arbor, MI: J. W. Edwards, pp. 233-236, 1952.