III. Working With A Graph

F. ZOOM and MEMORY

The ZOOM menu is a very useful tool when working with graphs. It not only offers preset windows, but other ways of looking at a graph. The MEMORY menu offers you a quick way to return to a window and to change the Zoom In and Zoom Out factors.

1: ZBox allows you to box in a part of the graph. This is useful when you need to look at a small part of the graph. ZPrevious will restore the previous window.

Example: Graph the function using ZOOM4 and then use ZBox to examine the graph close to the origin.

The graph is close to the x-axis around the origin,
so using ZBox will help with the analysis.
Access ZBox.
Hit ENTER and you will see the cursor
blinking at the origin.
Use the cursor keys to move the cursor to the indicated
point and hit ENTER. You will see the cursor change to
a rectangle. Once you hit enter,
that corner of the box is anchored
and cannot be moved.
Now move the cursor to the indicated value.
Now hit ENTER, and the graph will be redrawn
to show only the part inside the box.
Access MEMORY and select 1:ZPrevious
The graph is restored to the previous window.

2: Zoom In will zoom in on the graph with the position of the cursor serving as the new center. The default for Zoom In is a factor of 4, but this can be changed by accessing the MEMORY menu and using 4: SetFactors.

Example: Use the function from the previous example to access the Zoom In function and then use ZPrevious to restore the graph.

Graph the function.
Access the Zoom In key.
When you hit ENTER you
will see the cursor blinking
at the origin.
You can move the cursor to
any point that you want to be
the center of the new graph.
This has been left at the origin.
You can change the zoom in
factor by accessing MEMORY
and 4: SetFactors.
You can set these to any
number you need.

3: Zoom Out works exactly like Zoom In.

4: ZDecimal is a "friendly window" which means that TRACE moves in increments of 0.1. This is a useful window to use when the graph will fit because you can move to particular X-values easily. The use of this window is demonstrated in the polynomial examples in the Setting Windows section.

5: ZSquare will redraw the graph by adjusting [Xmin,Xmax] so that the tick marks are an equal distance apart on each axes. This is particularly useful when you need to see an accurate shape, such as a circle. ZDecimal is also a square window.

Example: Graph the circle by entering the functions and using ZStandard and ZSquare.

Enter the functions.
Use ZStandard.
Use ZSquare.

6: ZStandard is a preset window of [-10,10] by [-10,10] with tick marks set at integers. The use of this window is demonstrated in the polynomial examples in the Setting Windows section.

7: ZTrig is a trigonometry preset window with [Xmin,Xmax]=. This window is covered in the trigonometry examples in the Setting Windows section.

8: ZInteger will redraw the graph and reset the window to Xscl=10 and Yscl=10. The TRACE key will move in increments of 1.

Enter the function.
Use ZDecimal.
Access ZInteger.
Cursor will be at (0,0).
Press ENTER to
redraw the graph.
These are the new
window settings.

9: ZoomStat will change the graph window so that statistical points will all be shown. This window is generally not used in algebra, trigonometry or calculus.

10: ZoomFit will redraw the graph by resetting [YMin, YMax] to include the maximum and minimum values of the function over the interval [Xmin, Xmax]. This window can produce some rather distorted graphs and should be used with care.

Enter the function.
Use ZDecimal.
Use ZFit.
This is the new window.