How to use
Enter a function f (x) in the text input field marked "f(x)=".

 Example: f (x) = x2

Click the "Graph" button (this button also refreshes the graph).

Enter the derivative f '(x) in the text input field marked "f '(x)=".

 Example: f '(x)=2x

Select values for x1, x2, and c.

 Example: x1=0, x2=1, c=0.5

This can be done in either of two ways:

To erase the graph and all input fields (setting x1, x2, and c to default values), click the "Clear" button.
Examples
 Parabola: f (x) = x2, f '(x) = 2x,
x1=0, x2=1, c=0.5

 Exponential: f (x) = ex, f '(x) = ex,
x1=-1, x2=1, c=0.161439


Other Notes
The graph shows a secant line for f (x) through the points (x1,f (x1)) and (x2,f (x2)), and a tangent line through the point (c,f (c)). Labels with the text input fields also show the values of f (x1), f (x2), the slope of the secant line, and f (c). The Mean-Value Theorem states that, as long as f '(x) is continuous, there must be a value of c between x1 and x2 for which the secant line and the tangent line are parallel. This applet allows the user to experiment with the secant line and tangent line, attempting to find such a value for c.