Time Estimate Activity Main Idea 5 min (2:40) Each group completes one row of the table. All groups combine work in transparency form to complete the table as a class. Participants gather the data together and notice the pattern together and if it still holds true.
Step-by-step guide:

1. Have participants draw irregular polygons and fill in a similar chart. This time put the results on the overhead. Use the table on the opposite page for an overhead.

2. This table should look like the previous one; that is, there should be no difference in the angle sum if the polygons are irregular and/or concave.

Possible Problems and Concerns:
It may be very surprising to see that it makes no difference if the polygon is concave. Indeed, the mathematician on the algebra team that wrote these materials at first believed that it would make a difference.
Internet Resources:

https://mste.illinois.edu/m2t2/algebra/regs.gsp is a Geometer's Sketchpad file of regular polygons. Resources for this unit are available at https://mste.illinois.edu/m2t2/algebra/