Construct Regular Polygons with TI-84 Plus GeoMaster

By C. C. Edwards

A regular polygon is determined by its center and the number of its sides. You can use the GeoMaster DRAW menu on the TI-84 Plus graphing calculator to create regular and irregular polygons, circles, triangles, and many other basic geometric shapes. To construct a regular polygon, follow these steps:

  1. Press [GRAPH][WINDOW][7] to select the Reg Polygon tool from the DRAW menu.

    “Reg Polygon” in the upper-right corner of the screen indicates that the Reg Polygon tool is active.

  2. Use the arrow keys to move the cursor to the location on the screen where you want to place the center of the regular polygon. Press [ENTER] to anchor this point.

    As you move the cursor, its coordinates are displayed at the bottom of the screen.

  3. Press


    to display the number of sides of the polygon. The default number of sides is 6. Press [–] to decrease the number of sides of the polygon, or press [+] to increase the number of sides. Do not press [ENTER] when your polygon has the desired number of sides or you will be unable to rotate or adjust the size of the polygon.

    This is illustrated in the first screen for the construction of a pentagon. GeoMaster can construct polygons having a minimum of 3 sides and a maximum of 12 sides.


  4. Repeatedly press




    to adjust the size of your polygon and repeatedly press


    and/ or


    to rotate the polygon. Press [Enter] only when the polygon is to your liking.



    increases its size and


    decreases its size. This is illustrated in the second screen shown. Pressing


    rotates the polygon in the counterclockwise direction and


    rotates it in the clockwise direction. Continue using these arrow keys, in any order, until the polygon is exactly the way you want it. Press [ENTER] when you are done.

  5. Press [ENTER] or move the cursor away from the polygon.

    This is a crucial step. If it is not followed, then the last polygon you created may vanish when you ask GeoMaster to perform another operation. After doing this step, the polygon which appeared as dashed lines after performing Step 4 appears as solid lines. This indicates that your construction is now housed in the memory of the calculator.

After constructing your first regular polygon, the Reg Polygon tool remains active until you deactivate it. So if you want to construct more regular polygons, just repeat Steps 2 though 5. When you are finished using this tool, you deactivate it by pressing ë or by selecting another menu item.