First read Webster 1913's epicycloid writeup. The cardioid is the epicycloid for two circles of equal radius a. It is heart-shaped in appearance and has equation

(x2 + y2 - 2ax)2 = 4a2(x2 + y2).

Like all the epicycloids it is interesting from the point of view of gears. It is a special case of the limaçon of Pascal.

Car"di*oid (?), n. [Gr. () heart-sheped; herat + shape.] Math.

An algebraic curve, so called from its resemblance to a heart.

 

© Webster 1913.

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