Epicycloids {cardioid} can be curves traced by one circle point rolling on fixed equal-radius-circle outside: r = 2 * a * (l - cos(A)), where r is distance from pole, a is fixed-circle radius, pole is where rolling point meets fixed circle, and A is angle to radius. Cardioids have one loop and are special limaçon-curve cases.
Mathematical Sciences>Geometry>Plane>Curve>Kinds>Rolling
3-Geometry-Plane-Curve-Kinds-Rolling
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Date Modified: 2022.0224