How to Use a Ti84 Graphing Calculator to Find the Zero Function
The zero function, also referred to as "the zeros of a function," is the point on the Cartesian graph where a particular function crosses the X axis. This information is important because a function can cross the X axis up to as many times as the function has degrees. Furthermore, the zeros of a function will be the same values as the answers to the equations found after factoring the function.
Instructions

Press the graphing button in the upper left corner of the TI84. This will take you to the graphing screen.

Ensure all other previously entered equations are cleared.

Enter the function into the calculator.

Press the "Graph" button. This button is located in the upper right of the keypad, directly below the screen.

Ensure that your window settings are configured to allow for the entire function to be seen. Only the direction changes of the function are important.

Press the "Trace" button.

Use the arrow keys below the "Graph" button to move the cursor to every X position where the line crosses the X axis. Every point where Y equals zero is a "zero function." Take note of the X axis locations to verify any factoring that may be needed later. These zeros may also be verified using synthetic division if needed.