## Wednesday, March 20, 2013

### Day 116: Exterior Angles

I did a demo of the sum of the exterior angles in a polygon, recapped the exploration from yesterday, and set students to work on the first worksheet of Unit 8.

If you've never seen the demo, it's both simple and powerful. Draw a convex polygon on a piece of paper. Create one exterior angle at each vertex around the perimeter (be sure to work in the same direction around the exterior). Number and cut out each angle, making sure to note where the angle was on the cutout. The pieces easily reassemble into a central circle, showing the sum total to be 360.

This could have been done as a student activity and with more shapes to emphasize the independence of the relationship, but for time considerations I simply showed other examples in Geogebra and set the students to work.

I should note that we also pointed out how to determine the measure of a single interior or exterior angle IF the shape is regular. For some reason, this equation gave students fits for days.