How to Graph Functions on the TI-84 Plus

After you have entered functions into the TI-84 Plus calculator and formatted your graph, you’re almost ready to start your graphing fun. Once you get the hang of graphing, you won’t need to go through all these steps.

Turning off Stat Plots (if necessary)

The top line in the Y= editor tells you the graphing status of the Stat Plots. If Plot1, Plot2, or Plot3 is highlighted, then that Stat Plot will be graphed along with the graph of your functions. If it’s not highlighted, it won’t be graphed. In the first screen, Plot1 is highlighted and will be graphed along with the functions in the Y= editor.

To turn off a highlighted Stat Plot in the Y= editor, use the

keys to place the cursor on the highlighted Stat Plot and then press [ENTER]. See the second screen. The same process is used to highlight the Stat Plot again in order to graph it at a later time.

When you’re graphing functions, Stat Plots can be a nuisance if they’re turned on when you don’t really want them to be graphed. The most common symptom of this problem is the ERROR: INVALID DIMENSION error message — which by itself gives you almost no insight into what’s causing the problem. So if you aren’t planning to graph a Stat Plot along with your functions, make sure all Stat Plots are turned off!

Selecting and deselecting a function on the TI-84 Plus

Deselect (turn off) Y₁ and Y₂ by removing the highlight from their equal signs. This is done in the Y= editor by using the

keys to place the cursor on the equal sign and then pressing [ENTER] to toggle the equal sign between highlighted and not highlighted. The calculator graphs a function only when its equal sign is highlighted!

Do you see the difference between the two screens?

Adjusting the TI-84 Plus graph window

When you graph a function, you usually can’t see the whole graph. You are limited to viewing the graphing window, which typically shows only a small portion of the function. There are four values that determine the portion of the coordinate plane you can see: Xmin, Xmax, Ymin, and Ymax. Press [WINDOW] to display the current window variables.

It takes practice to find a good viewing window for the function you’re graphing. Here are the steps needed to set the window of your graph:

1. Press [WINDOW] to access the Window editor.

2. After each of the window variables, enter a numerical value that is appropriate for the functions you’re graphing. Press e after entering each number.

   Entering a new window value automatically clears the old value.

   Make sure your (Xmin < Xmax) and (Ymin < Ymax) or you’ll get the ERROR: WINDOW RANGE error message.

   Editing your Window variables is a good place to start as you search for a good viewing window. In addition, using the Zoom features may be necessary to perfect your graphing window. The following gives an explanation of the variables you must set to adjust the graphing window:

   • Xmin and Xmax: These are, respectively, the smallest and largest values of x in view on the x-axis.

     If you don’t know what values your graph will need for Xmin and Xmax, press [ZOOM][6] to invoke the ZStandard command. This command automatically graphs your functions in the Standard viewing window.

   • Xscl: This is the distance between tick marks on the x-axis. (Go easy on the tick marks; using too many makes the axis look like a railroad track. Twenty or fewer tick marks makes for a nice looking x-axis.)

     If you want to turn off tick marks altogether, set Xscl=0 and Yscl=0.

   • Ymin and Ymax: These are, respectively, the smallest and largest values of y that will be placed on the y-axis.

     If you have assigned values to Xmin and Xmax but don’t know what values to assign to Ymin and Ymax, press [ZOOM][0] to invoke the ZoomFit command. This command uses the Xmin and Xmax settings to determine the appropriate settings for Ymin and Ymax, and then automatically draws the graph.

   • Yscl: This is the distance between tick marks on the y-axis. (As with the x-axis, too many tick marks make the axis look like a railroad track. Fifteen or fewer tick marks is a nice number for the y-axis.)

   • Xres: This setting determines the resolution of the graph. It can be set to any of the integers 1 through 8. When Xres is set equal to 1, the calculator evaluates the function at each of the 133 pixels on the x-axis and graphs the result. If Xres is set equal to 8, the function is evaluated and graphed at every eighth pixel.

     Xres is usually set equal to 1. If you’re graphing a lot of functions, it may take the calculator a while to graph them at this resolution. If you change Xres to a higher number, your function will graph quicker, but you may not get as accurate of a graph.

   • TraceStep and

     

     These two variables are linked together, and TraceStep is always twice as big as

     

     value, which determines how your cursor moves on a graph screen in “free trace.” TraceStep controls the X-value jump when you are tracing a function on a graph screen.

3. Press [GRAPH] to graph the functions.

Stopping or pausing your TI-84 Plus graph

After pressing [GRAPH], there’s usually a small delay before you begin to see your function plotting on the graph from left to right. If it’s taking a long time for the calculator to graph your functions (maybe your Xres setting is too small), press [ON] to terminate the graphing process.

Simply press [ENTER] to pause the plotting of your graph and then press [ENTER] again to resume graphing. See the following two screens. Notice, the elliptical busy indicator in the top right corner of the screen indicating that your calculator is working hard.