One can find the straight-line distance between two given points on the graph of a function from the graph window. First enter and graph a function. For example, we determine the distance between the points determined by x = 1 and x = 3 on the graph of .

First, enter the function in the Y= editor as function y1. Then press to access the Zoom menu, then select 6: ZoomStd. The graph of appears in the standard viewing window.

From the graph window, press to access the Math menu. Then select 9: Distance. The 1st Point? prompt appears. Press to define the left endpoint of the straight line. Then the 2nd Point? prompt appears. Press to define the right endpoint of the straight line. The TI-89 marks the two points (if the points are in the graph viewing window) and displays the distance between the two indicated points at the bottom of the screen.

You'll probably want to adjust the window for a closer view. Press WIN (located above the F2 key) to define a more suitable viewing window; say, xmin = 0, xmax = 3, xscl = 1, ymin = -5, ymax = 10, yscl = 2. Then press GRAPH (located above the F3 key). The graph appears. Now determining the straight-line distance from x=1 to x=2 yields a closer view. In setting the window, remember to allow space at the bottom of the screen for displaying the answer.