In Cabri Jr., a geometry application for the TI-84 Plus calculator, a perpendicular bisector can be constructed to an already existing line, segment, or side of a triangle/polygon.

To construct a perpendicular bisector, follow these steps:

1. Press [ZOOM][3] to select the Perp. Bis. tool from the F3 menu.

A picture of the Perp. Bis. tool appears in the upper-left corner of the screen.

2. Use the arrow keys to move the cursor to any point of the already constructed line.

The line or segment appears as a moving dashed line and the cursor changes to a solid arrow.

3. Press [ENTER] to construct the perpendicular bisector.

After constructing a perpendicular bisector, the Perp. Bis. tool remains active until you deactivate it. So if you want to construct more perpendicular bisectors, just repeat Steps 2 and 3. When you are finished using the tool, you deactivate it by pressing [CLEAR] or by selecting another menu item.

For Cabri Jr. to recognize the existence of an angle, that angle must contain three defining points: the vertex and a point on each side of the angle. Also, Cabri Jr. recognizes a point only if it appears on the screen as a small square. If the angle you wish to bisect does not contain the small squares representing these three defining points, then Cabri Jr. cannot bisect it.

To construct the bisector of an already constructed angle containing three defining points, follow these steps:

1. Press [ZOOM][4] to select the Angle Bis. tool form the F3 menu.

A picture of the Angle Bis. tool appears in the upper-left corner of the screen.

2. Use the arrow keys to move the cursor to an existing point on one side of the angle and press [ENTER] to anchor that point.

You know that the cursor has reached that when the point starts blinking.

3. Use the arrow keys to move the cursor to the vertex of the angle and press [ENTER] to anchor the vertex.

The vertex must always be the second point that defines the angle.

4. Use the arrow keys to move the cursor to an existing point on the other side of the angle and press [ENTER] to anchor that point.

The angle bisector appears as a solid line, indicating that your construction is complete.

After constructing an angle bisector, the Angle Bis. tool remains active until you deactivate it. So if you want to construct more angle bisectors, just repeat Steps 2 through 4. When you are finished using the tool, you deactivate it by pressing [CLEAR] or by selecting another menu item.