- a plane curve generated by the locus of the point at which a variable tangent to a rectangular hyperbola intersects a perpendicular from the center to the tangent. Equation: r2 = 2a2cosθ.
- a closed plane curve consisting of two symmetrical loops meeting at a node. Equation: (x ² + y ²)² = a ²(x ² – y ²), where a is the greatest distance from the curve to the origin. The symbol for infinity (∞) is an example
