The TI-84 Plus graphing calculator can do only what you tell it to do — which doesn’t always produce an accurate graph. Following are the three main causes of inaccurate graphs, and their solutions:

• The graph is distorted by the size of the screen.

Because the calculator screen isn’t square, circles don’t look like circles unless the viewing window is properly set. How do you properly set the viewing window? No problem! Just graph the function, and then press [ZOOM][5] to invoke the ZSquare command.

ZSquare readjusts the window settings for you and graphs the function again in a viewing window in which circles look like circles.

• The viewing window is too small or too big.

If you don’t know what the graph should look like, then after graphing it you should zoom out to see more of the graph or zoom in to see a smaller portion of the graph. To do this, press [ZOOM][3] to zoom out, or press [ZOOM][2] to zoom in.

Then use the

keys to move the cursor to the point from which you want to zoom out or in, and press [ENTER]. It’s just like using a camera. The point you want to move the cursor to is the focal point.

After zooming in or out, you may have to adjust the window settings.

As an example, follow the progression of graphing Y1.

It was first graphed in the Standard viewing window. Then it was zoomed out from the point (0, 10). And finally, the window settings were adjusted to get a better picture of the graph.

• Vertical asymptotes may not be recognizable.

In all graph styles except Animate and Dotted Line, the calculator graphs one point, and then the next point, and connects those two points with a line segment. This sometimes causes vertical asymptotes to appear on the graph. The last graph illustrates an example of when a vertical asymptote is present. Don’t mistake this almost-vertical line for a part of the graph. It’s not; it’s just a vertical asymptote.

In a different viewing window, the vertical asymptote may not even appear. This happens when the calculator graphs one point, but the next point is undefined because the x value of that point is exactly at the location of the vertical asymptote. Here is an example of re-graphing the last graph, using a viewing window in which the vertical asymptote does not appear.