Cardioid
Summary:
For r = a + b cos θ and r = a + b sin θ,
When | a | > 2 | b |, the curve is convex, e.g. r = 1 + 0.4 cos θ.
When | b | < | a | < 2 | b |, the curve has an indentation, e.g. r = 1 + 0.6 cos θ.
For | a | ≤ | b |, the curve has a cusp, e.g. r = 1 + cos θ.