View Function and Graph on Same TI84 Plus Screen
If you’re planning to play around with the definition of a function you’re graphing on your TI84 Plus calculator, it’s quite handy to have both the Y= editor and the graph on the same screen. That way you can edit the definition of your function and see the effect your editing has on your graph. To do so, follow these steps:

Put the calculator in Horizontal mode.
Press [MODE] and highlight Horizontal in the ninth line of the menu, as illustrated in the first screen.
To highlight an item in the Mode menu, use the arrow keys to place the cursor on the item, and then press [ENTER].
You may notice that the graphing window dimensions have not changed, but the graph now only takes up half of the screen. Having a smaller graphing window is the price you pay for viewing the Y= editor on the same screen. If you don’t like the look of the graph, try pressing [ZOOM][5] to square the graphing window.

Press [Y=].
The Graph window appears at the top of the screen and the Y= editor at the bottom of the screen.

Enter or edit a function in the Y= editor.
See the second screen.

Press [GRAPH] to graph the function.
The graph doesn’t update after entering a function in the Y= editor. You must press [GRAPH] to update the graphing screen. See the third screen.
To edit or enter a function, press [Y=]. To see the resulting graph, press [GRAPH].