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


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Ensure all other previously entered equations are cleared.


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Enter the function into the calculator.

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

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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.

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Press the "Trace" button.

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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.

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