The applet illustrates the geometric interpretation of the derivative.
Click the screen shot below to open the applet in a new window:
The user can enter a formula and the applet will graph an arbitrary function. The user can sketch the derivative of the function by drawing on screen with the mouse. The actual graph of the derivative is revealed point by point as the user drags a slider. At the same time, the lineal element representing the tangent line and its slope is dynamically shown. Many demo examples are provided.