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: r^{2} = 2 a^{2} cosθ.
a closed plane curve consisting of two symmetrical loops meeting at a node. Equation: (x² + y²)² = a²(x² – y²), where a is the greatest distance from the curve to the origin. The symbol for infinity (∞) is an example