IV. Special Graphs

A. Derivative

In calculus it can be very useful to see the graph of a derivative. The TI-89 will draw the graph of the derivative of a function. You will need to use the nDeriv function which is found in the MATH/Calculus menu.

You can use the graph of the derivative to determine where the function is increasing (derivative is positive) and where the function is decreasing (derivative is negative), and where the function has a maximum or minimum (where the derivative is zero or undefined). The graph of the derivative may take a few moments to draw. This is because the calculator is using numerical approximation to determine the derivative values. Once the derivative is drawn, you can use Trace, TABLE, etc, on the graph.

Press to access the Y=Editor. Enter the function and the derivative.
Use TABLE to help find a window. Press and enter some values for x.
Set a WINDOW. Press .
From the Y=Editor screen press to access the STYLE menu. Select 4:Thick for the derivative graph.
Press to draw the graphs.