Texas Instruments TI-82 Keystroke Manual page 51

46 Calculator Keystroke Guide
XFact and YFact are the factors by which the calculator will zoom in or out in the x- and y-
directions, respectively, when the Zoom In or Zoom Out options are chosen from the Zoom menu.
The calculator comes from the factory with a default setting of 4 for each of these variables. If
you zoom in on the x-axis by a factor of 4, the distance represented by the width of the calculator
graphing screen in the resulting viewing window will only be ¼ as great as it was before. If you
zoom out on the x-axis by a factor of 4, the distance represented by the width of the calculator
graphing screen in the resulting viewing window will be 4 times as great as it was before. The
values of XFact and YFact may be changed by using the arrow keys and typing in new settings.
For now, set both XFact and YFact equal to 4, if they are not 4 already. If you wish to return to
the Home screen, press 2nd [QUIT].
= −
To see how Zoom In works, first enter as Y the equation y 2 x 1 and enter as Y the
1 2
= − +
2
equation y x x 1 3 . . Graph these equations in the Standard viewing window.
Notice that it appears that these two graphs intersect in the first quadrant, but perhaps it would be
good to get a closer look. Press the ZOOM key and choose 2 (Zoom In). The calculator returns to
the Graph screen, which appears unchanged. Before zooming in, the calculator needs to know
what part of the Graph screen you wish to zoom in on. A free-moving cursor appears near the
origin. (You may have to look closely to see it.) You use the arrow keys to move this cursor to the
point that you would like to have in the center of the Graph screen after the calculator zooms in.
Since you want to get a better look at where the two graphs appear to intersect, use the arrow
keys to move the cursor to the place on the screen where the graphs appear to intersect.
To make the zoom in occur, press ENTER. The graphs are redrawn, zoomed in on the point of
interest. The graphs still appear as though they may intersect. Notice that the Zoom In cursor still
appears on the screen. To zoom in again on the place where the graphs appear to intersect, use the
arrow keys again to move the cursor over the place where the graphs appear to intersect and press
ENTER. From the resulting zoomed in view, it seems that these two graphs don't intersect after all!
If you want to zoom in again, just to be sure, follow the same procedure.