TI-84 Plus CE field manual for IB Math
Reading a graph: trace and zoom
Move a cursor along a plotted curve to read coordinates from it, and use the zoom menu to choose the viewing window deliberately.
Trace the graph of y=x−32x+1 to read coordinates from it, and use the window to locate its vertical asymptote.
Trace moves a cursor along the curve. Graph the function on the standard window, then press . A cursor appears on the curve, and the bottom of the screen shows its X= and Y= coordinates. and move the cursor along the curve, and and switch between curves when more than one is plotted. The top-left corner names the function the cursor is on.
Trace moves in fixed steps, which sets its precision. Each press moves the cursor by the window width divided by 132: two columns of the 265-pixel graph area, listed as TraceStep on the screen. On the standard window that is 20÷132≈0.152, so one pass of trace pins an x-value down to about 0.15: roughly one significant figure. To read more precisely, shrink the window rather than pressing the arrow more carefully.
Typing a number jumps the cursor directly there. While tracing, type a value and press , and the cursor moves to that x-coordinate without walking to it.
The zoom menu, opened with , changes the window for you. The entries worth knowing:
- 1: ZBox draws a rectangle: move to one corner, press , move to the opposite corner, press , and the window becomes that rectangle. In the screen below, the dashed box around the left branch becomes the new window.
- 2: Zoom In and 3: Zoom Out quarter or quadruple the visible range about the cursor, by a factor of 4 each press.
- 6: ZStandard resets the window to −10 to 10 on both axes.
- 0: ZoomFit keeps the x-range and chooses a y-range that fits the curve, which corrects a graph that appears as a flat line along one edge.
For a window that a question specifies exactly, type it directly with instead.
Now locate the vertical asymptote. Trace rightwards towards x=3: at x≈2.88 the readout shows y=−55.75, and one press later, at x≈3.03, it shows y=233. A jump from a large negative value to a large positive one within a single step means the asymptote lies between those two x-values.
Narrow the window by hand, not with a box. Near the asymptote the curve plunges far outside any small y-range, so a Zoom Box drawn there would contain no curve at all. Instead press and type the bracket into x while opening y wide: Xmin=2.95, Xmax=3.04, Ymin=-1000, Ymax=1000. Both branches stay on screen. Press again: the jump now happens between x≈2.9998 (y≈−30800) and x≈3.0005 (y≈15400), so one round has narrowed the bracket from about 0.15 to about 0.0007.
One setting matters here. Press for FORMAT and turn Detect Asymptotes on. When it is off, the calculator draws a false steep line across the asymptote, and trace will report ordinary-looking coordinates along that line. Turning it on makes graphs draw slightly more slowly and removes the false line.
The vertical asymptote is at x=3.00 to 3 s.f. To read any value from a graph more precisely, narrow the window and trace again.