# Interior Angles of Polygons

(use with UCSMP Geometry, Lesson 3-1)

If you can't see the demo above, click here.

## Directions:

Try to investigate the sum of the interior angles of a polygon. Click on the midpoint of a side of the polygon to rotate a copy of the polygon around the midpoint. You can then drag any of the red points and the rotation(s) will update dynamically. To change the kind of polygon you are investigating, select the number of desired sides at the bottom. To start measuring angles, click the button SELECT VERTEX and the sum of the measures of all the angles with that point as a vertex will appear in the table to the right. Any angle that gets added to that vertex will get added to the table. After selecting the point, click the SELECT VERTEX button again to disable the selection mode. If you accidentally click the wrong midpoint you can use the REMOVE LAST POLYGON button to undo.