Definition of a critical point. Above the level of most students. useful for tutors.
MathWorld

A helpful scientific calculator that runs in your web browser window.
Holt Online Learning

Excellent site showing examples of algebra, trig, calculus, differential equations, and linear algebra.
Paul's Online Math Notes

JAVA Applet for plotting curves defined in rectangular or parametric form.
MIT

Using parametric equations to define a curve in two or three dimensions and properties of parametric equations.
MIT

differentiation formulas
StudyStack

A website that lays out the theory of working with partial derivatives.
Mathworld Wolfram

Gives detailed explanation on working with partial derivatives. This site also provides examples that students can work through and check.
Analyze Math
