Texas Instruments TI-92 Getting Started page 17

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Graphing Technology Guide: TI-92
Figure 5.49: ZOOM FACTORS menu
Technology Tip: An advantage of zooming in from square viewing window is that subsequent windows will also be
square. Likewise, if you zoom in from a friendly viewing rectangle, the zoomed windows will also be friendly.
The default zoom factor is 4 in both direction. It is not necessary for xFact and yFact to be equal. Sometimes, you
may prefer to zoom in one direction only, so the other factor should be set to 1. Press ESC to leave the ZOOM
FACTORS menu and go back to the graph. (Pressing 2nd QUIT will take you back to the Home screen.)
Technology Tip: The TI-92 remembers the window it displayed before a zoom. So if you should zoom in too much
and lose the curve, press F2[Zoom] B[Memory] 1[ZoomPrev] to go back to the window before. If you want to
execute a series of zooms but then return to a particular window, press F2[Zoom] B[Memory] 2[ZoomSto] to store
the current window's dimensions. Later, press F2[Zoom] B[Memory] 3[ZoomRcl] to recall the stored window.
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5.2.7 Relative Minimums and Maximums: Graph y = –x + 4x once again in the standard viewing rectangle. This
function appears to have a relative minimum near x = –1 and a relative maximum near x = 1. You may zoom and
trace to approximate these extreme values.
First trace along the curve near the local minimum. Notice by how much the x-values and y-values change as you
move from point to point Trace along the curve until the y-coordinate is as small as you can get it, so that you are as
close as possible to the local minimum, and zoom in (press F2[Zoom] 2[Zoomln] ENTER or use a zoom box).
Now trace again along the curve and, as you move from point to point, see that the coordinates change by smaller
amounts than before. Keep zooming and tracing until you find the coordinates of the local minimum point as
accurately as you need them, approximately (–1.15, –3.08).
Follow a similar procedure to find the local maximum. Trace along the curve until the y-coordinate is as great as
you can get it, so that you are as close as possible to the local maximum, and zoom in. The local maximum point on
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the graph of y = –x + 4x is approximately (1.15, 3.08).
The TI-92 can automatically find the maximum and minimum points. While viewing the graph, press F5[Math] to
display the Math menu (Figure 5.50). Choose 3[Minimum] to calculate the minimum value of the function and
4[Maximum] for the maximum. You will be prompted to trace the cursor along the graph first to a point left of the
minimum/maximum (press ENTER to set this lower bound). Note the arrow near the top of the display marking the
lower bound (as in Figure 5.51).
Figure 5.50: Math menu Figure 5.51: Finding a minimum
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