Texas Instruments TI-92 Getting Started page 15

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Graphing Technology Guide: TI-92
screen. Next press the left and right arrow keys to trace along the graph of y = –.25x. When more than one function
is plotted, you can move the trace cursor vertically from one graph to another with the and, directions.
Technology Tip: By the way, trace the graph of y = –.25x and press and hold either the or direction. The
cursor becomes larger and pulses as it moves along the graph. Eventually you will reach the left or right edge of the
window. Keep pressing the direction and the TI-92 will allow you to continue the trace by panning the viewing
rectangle. Check the WINDOW screen to see that the xmin and xmax are automatically updated.
The TI-92 has a display of 239 horizontal columns of pixels and 103 vertical rows, so when you trace a curve across
a graph window, you are actually moving from xmin to xmax in 238 equal jumps, each called ∆x. You would
−
xmax xmin
calculate the size of each jump to be ∆x = . Sometimes you may want the jumps to be friendly
238
numbers like 0.1 or 0.25 so that, when you trace along the curve, the x-coordinates will be incremented by such a
convenient amount. Just set your viewing rectangle for a particular increment ∆x by making xmax = xmin + 238 ·
∆x. For example, if you want xmin = –5 and ∆x = 0.3, set xmax = –5 + 238 · 0.3 = 66.4. Likewise, set ymax = ymin
+ 102 ∆y if you want the vertical increment to be some special ∆y.
To center your window around a particular point, say (h, k), and also have a certain ∆x, set xmin = h – 119 · ∆x and
make xmax = h + 119 · ∆x. Likewise, make ymin = k – 51 · ∆y and make ymax = k + 51 · ∆y. For example, to
center a window around the origin (0, 0), with both horizontal and vertical increments of 0.25, set the range so that
xmin = 0 – 119 · 0.25 = –29.75, xmax = 0 + 119 · 0.25 = 29.75, ymin = 0 – 51 · 0.25 = –12.75 and ymax = 0 + 51 ·
0.25 = 12.75.
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See the benefit by first plotting y = x + 2x + 1 in a standard graphing window. Trace near its y-intercept, which is
(0, 1), and move towards its x-intercept, which is (–1, 0). Then press F2[Zoom] 4[ZoomDec] and trace again near
the intercepts.
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5.2.6 Zoom: Plot again the two graphs, for y = –x + 4x and y = –.25x . There appears to be an intersection near x =
2. The TI-92 provides several ways to enlarge the view around this point. You can change the viewing rectangle
directly by pressing WINDOW and editing the values of xmin, xmax, ymin, and ymax. Figure 5.42 shows a new
viewing rectangle for the range displayed in Figure 5.41. The cursor has been moved near the point of intersection;
move your cursor closer to get the best approximation possible for the coordinates of the intersection.
Figure 5.41: New WINDOW Figure 5.42: Closer view
A more efficient method for enlarging the view is to draw a new viewing rectangle with the cursor. Start again with
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+ 4x and y = –.25x in a standard viewing rectangle. (Press F2[Zoom]
a graph of the two functions y = –x
6[ZoomStd] for the standard viewing window.)
Now imagine a small rectangular box around the intersection point, near x = 2. Press F2[Zoom] 1[ZoomBox]
(Figure 5.43) to draw a box to define this new viewing rectangle. Use the arrow keys to move the cursor, whose
coordinates are displayed at the bottom of the window, to one corner of the new viewing rectangle you imagine.
Press ENTER to fix the corner where you moved the cursor; it changes shape and becomes a blinking square
(Figure 5.44). Use the arrow keys again to move the cursor to the diagonally opposite corner of the new rectangle
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