How to Enter Functions on TI83 Plus
Before you can graph a function, you must enter it into the TI83 Plus calculator. The calculator can handle up to ten functions at once, Y_{1} through Y_{9} and Y_{0}. To enter functions in the calculator, perform the following steps:

Press [MODE] and put the calculator in Function mode.
To highlight an item in the Mode menu, use the
keys to place the cursor on the item, and then press [ENTER]. Highlight Func in the fourth line to put the calculator in Function mode.

Press [Y=] to access the Y= editor.

Enter the definitions of your functions:
To erase an entry that appears after Y_{n}, use the
keys to place the cursor to the right of the equal sign and press [CLEAR]. Then enter your definition for the new function and press [ENTER].
When you’re defining functions, the only symbol the calculator allows for the independent variable is the letter X. Press
to enter this letter in the definition of your function.
As a timesaver, when entering functions in the Y= editor, you can reference another function in its definition. To paste a function name in the function you’re entering in the Y= editor, follow these steps:

Press
to access the YVariables menu.

Press [1] to access the Function menu.

Press the number key for the name of the function you want to paste in the definition.