A cusp is a point on a continuous curve where the tangent vector reverses sign as the curve is traversed. A function has a cusp (also called a Spinode) at a point if is Continuous at and from one side while from the other side, so the curve is Continuous but the Derivative is not. A cusp is a type of Double Point. The above plot shows the curve , which has a cusp at the Origin.

**References**

Walker, R. J. *Algebraic Curves.* New York: Springer-Verlag, pp. 57-58, 1978.

© 1996-9

1999-05-25