Cardioid
A curve that is somewhat heart shaped. A cardioid can
be drawn by tracing the path of a point on
a circle as the circle
rolls around a fixed circle of the
same radius.
The equation is usually written in polar
coordinates.
Note: A cardioid is a special case of the limaçon
family of curves.
Cardioid: r = a ± a cos θ (horizontal)
or r = a ± a sin θ (vertical)
r = 2 + 2 cos θ 
r = 2 + 2 sin θ 
See
also
Polar
curves, cycloid
