Two Dürer's Foliums

Dürer's folium is a special epitrochoid. This Demonstration shows how two such curves, with one of them rotated by 90°, are defined by rolling two small circles of radius over a larger circle of radius .
The "phase" control draws the curves; the "transparency" control shows the three points and circles.
The folium is also the inverse of Delanges's trisector, and thus can be used to trisect angles.


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