A curve traced by a point on the circumference of a circle as that circle rolls along the outside of another circle.
From Greek 'epi' (upon) + 'kyklos' (circle) + '-oid' (resembling). The term entered mathematics in the 17th century as calculus developed and mathematicians studied rolling curves.
Epicycloids create stunning petal-shaped curves, and they're exactly the same principle behind spirograph drawings—one of the most satisfying toys ever invented shows off genuine mathematical beauty!
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