http://www.qwiki.com/embed/Derivative
Qwiki is a great way to update whatever knowledge you need to refresh. I just looked at Calculus, Diferential calculus, Integral, Lambda calculus and LINQ.
I like the synchronized voice and the text and the functions and mathematicans appearing. Great learning tool!
A post from qwiki.com by has the whole story. Here is a part:
At each point, the line is always tangent to the curve. Its slope is the derivative; the positivity, negativity and zeroes of the derivative are marked by green, red and black respectivelyQwikis in this Qwiki
In calculus, a branch of mathematics, the derivative is a measure of how a function changes as its input changes. Loosely speaking, a derivative can be thought of as how much one quantity is changing in response to changes in some other quantity; for example, the derivative of the position of a moving object with respect to time is the object’s instantaneous velocity. Conversely, the integral of the object’s velocity over time is how much the object’s position changes from the time when the integral begins to the time when the integral ends. The most common approach to turn this intuitive idea into a precise definition uses limits, but there are other methods, such as non-standard analysis.
Morten Jacobsen 