The hypocycloid and its relatives

A hypocycloid is a curve formed by the path of a point attached to a smaller circle as it rolls around inside a larger circle. Related curves are the hypotrochoid, epicycloid and epitrochoid.
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[@jimiwills]

I love spirograph! I find it interesting to think about the epicycloid when a=0

[@ujjwalathukral398]

Lovely explanation