Dupin's Indicatrix
A pair of conics obtained by expanding an equation in Monge's Form 
in a Maclaurin Series
This gives the equation
Amazingly, the radius of the indicatrix in any direction is equal to the Square Root of the Radius ofCurvature in that direction (Coxeter 1969).
References
Coxeter, H. S. M. ``Dupin's Indicatrix'' §19.8 in Introduction to Geometry, 2nd ed. New York: Wiley, pp. 363-365, 1969.
- Independent Vertices
- Indeterminate Problems
- Index
- Index Set
- Index Theory
- Indicatrix
- Indicial Equation
- Indifference Principle
- Induced Map
- Induced Norm
- Induction
- Induction Axiom
- Induction Principle
- Inequality
- Inexact Differential
- Inf
- Infimum
- Infimum Limit
- Infinary Divisor
- Infinary Multiperfect Number
- Infinary Perfect Number
- Infinite
- Infinite Product
- Infinite Series
- Infinite Set