You can construct perpendicular or parallel lines in the Cabri Jr. geometry application on the TI-84 Plus calculator. To construct such lines, you have to start with an already constructed line, segment, or side of a triangle/polygon.

To construct a line that is perpendicular or parallel to an already constructed line, segment, or side of a triangle/polygon, follow these steps:

1. Select the appropriate tool from the F3 menu.

To do this, press [ZOOM]. Use

to move the cursor to the tool you wish to use and press [ENTER]. A picture of the tool you selected appears in the upper-left corner of the screen. The first picture illustrates that the Perp tool is active and waiting for you to construct a perpendicular line.

2. Use the arrow keys to move the cursor to the already constructed line, segment, or side of a triangle/polygon.

The line or segment appears as a moving dashed line and the cursor changes to a solid arrow, as illustrated in the first picture.

3. Press [ENTER].

A perpendicular line appears at the location of the cursor, as illustrated in the second picture. It appears as a dotted line, indicating that it has not yet been placed where you want it.

4. If necessary, use the arrow keys to move the line to the location on the screen where you wish to construct the perpendicular or parallel line. Press [ENTER] to anchor this location.

If you are moving the line to an already constructed point, you know you have reached that point when the point begins to blink. Press [ENTER] when the line is at the desired location. The third picture illustrates this step when constructing a perpendicular line.

After constructing a parallel or perpendicular line, the tool you were using remains active until you deactivate it. So if you want to construct more objects of the same kind, just repeat Steps 2 through 4. When you are finished using that tool, you deactivate it by pressing [CLEAR] or by selecting another menu item.