Find the Slope of a Curve on TI-83 Plus - dummies

Find the Slope of a Curve on TI-83 Plus

By C. C. Edwards

The TI-83 Plus graphing calculator is not equipped to find the derivative of a function. But it 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:

  1. 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.

  2. Set the Format menu to ExprOn and CoordOn.

  3. Press [2nd][TRACE] to access the Calculate menu.

  4. Press [6] to select the dy/dx option.

  5. If necessary, repeatedly press


    until the appropriate function appears at the top of the screen.

  6. 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=. 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, and then instead of entering a value of x, just use the




    to move the cursor to the desired location on the graph of the function.

  7. Press [ENTER].

    After pressing [ENTER], the slope (derivative) is displayed at the bottom of the screen.