In calculus, you need to graph the derivative of a function in order to find its critical points, which you can do on your TI-84 Plus calculator. Just follow these steps:
Enter your functions in the Y= editor.
Use the arrow keys to place your cursor in an open equation in the Y= editor.
Press [MATH] to access the nDeriv template.
then press [ALPHA][TRACE] and choose your function, then press the right arrow and
See the first screen. This is a sneaky move. You aren't using the nDeriv( template to take the derivative at a specific x-value. Instead, by taking the derivative at x = x, you are taking the derivative at all points where the function is defined.
Press [GRAPH] to display the graph of your function and the derivative of the function.
See the second screen.
Press [2nd][TRACE] to access the Calculate menu.
Press  to select the zero option.
If necessary, repeatedly press the up- and down-arrow keys until the derivative function appears in the border at the top of the screen.
Don’t forget to do this step!
Enter the Lower and Upper Bounds, then a guess and press e.
This is illustrated in the third screen.