Find the Slope of a Curve with the TI-84 Plus
The TI84 graphing calculator is not equipped to find the derivative of a function. For example, it cannot tell you that the derivative of x2 is 2x. But the calculator is equipped with a numerical routine that evaluates the derivative at a specified value of x.
This numerical value of the derivative is the slope of the tangent to the graph of the function at the specified x-value. It is also called the slope of the curve. To find the slope (derivative) of a function at a specified value of x, perform the following steps:
Graph the function in a viewing window that contains the specified value of x.
To get a viewing window containing the specified value of x, that value must be between Xmin and Xmax.
Set the Format menu to ExprOn and CoordOn.
Press [2nd][TRACE] to access the Calculate menu.
Press  to select the dy/dx option.
If necessary, repeatedly press
until the appropriate function appears at the top of the screen.
This is illustrated in the first graph shown here.
Enter the specified value of x.
To do so, use the keypad to enter the value of x. As you use the keypad, X= appears, replacing the coordinates of the cursor location appearing at the bottom of the screen in the previous step. The number you key in appears after X=. This is illustrated in the second graph. If you make a mistake when entering your number, press [CLEAR] and re-enter the number.
If you are interested only in finding the slope of the function in a general area of the function instead of at a specific value of x, instead of entering a value of x, just use the
to move the cursor to the desired location on the graph of the function.
After pressing [ENTER], the slope (derivative) is displayed at the bottom of the screen. This is illustrated in the third graph here.