III. Working With A Graph

A. TRACE

TRACE is a very useful tool in graph analyses. Even when a graph is not visible, you can use TRACE to find Y-values. When using TRACE, the X-values are restricted to the interval [Xmin, Xmax]. For values outside of that interval you will have to change the window or use TABLE. However, the Y-values are not restricted to [Ymin,Ymax].

Locate TRACE.
X-values are restricted
to [Xmin,Xmax].
You will get an error
if you enter an X
beyond the set Window.

You can use the left and right cursors to trace along a curve or you can enter a value of x by hitting the TRACE key and then a numerical value. If you use the cursors to trace along the curve, the graph will be redrawn as you move beyond the set window and the window will change accordingly.

Example 1: Enter the function y=x(x+1)(x-2) and graph using ZOOM4.

Hit TRACE.
Cursor is at (0,0).
Use the cursor
to move to x=.5
Enter the value x=1.
Press Enter.
For x=4 the Y-value
is not shown on the graph.
For x=-6, there is
an error message.

Example 2: In this example, the y-values are so small that the graph does not show on the screen. However, the TRACE key can still be used to find Y-values.

Enter the function.
Use ZOOM4
Enter TRACE
and then 1.

ZOOM4 is called a friendly window because TRACE moves in increments of x=0.1. For other windows, the TRACE will most likely not move to a value you want, so you can just enter the x-value you desire.