In geometry, a hypocycloid's a special plane curve generated by the trace of a fixed point on a small circle that rolls within a larger circle. It's comparable to the cycloid but instead of the circle rolling along a line, it rolls within a circle. If the smaller circle has radius r, and the larger circle has radius R = kr, then the parametric equations for the curve can be given by either: » x ( heta) = (R - r) cos heta + r cos left(frac heta ight), or: » x ( heta) = r (k - 1) cos heta + r cos… (More on Hypocycloid)