## Sunday, June 14, 2015

### Sum of Exterior Angles of a Polygon Lite.

There is a nice little app which I might have talked about before but I took time to explore it more so I decided to review it.  It is the Sum of the Exterior Angles of a Polygon Lite  is the free version of the 99 cent app.

When you first open up the app you see this triangle with angles and a play button.  There is no real information until you hit the play button.  Once you tap the play button, the app opens up and you see a brief animation which introduces students to how you identify the exterior angles.    It is a nice introduction to the topic.

After the introduction, a blank work space appears with instructions for using it.  You use your fingers to create the polygon by taping on the space for the vertex.  You can create any polygon from a triangle on up.  There is an erase button at the bottom and a slider to the right that is used after the shape is drawn.

It automatically forms the exterior angles once the polygon is drawn as seen in the photo to the right.  When you move the slider down, the sides move closer and closer together until they disappear and the exterior angles form a 360 degree circle.

This allows students to see why the sum of exterior angles is 360 degrees.  Furthermore, when you are ready to do another polygon, you hit the erase button and draw the next one.  It is easy to create regular polygons.  What is even neater is that there is a work sheet for students to do that is found by clicking on one of the buttons and the button next to it shows the same worksheet with possible answers.

I plan on using this when we do the sum of exterior angle theorem in Geometry.  It is a nice way to let students explore the topic before the theorem is taught and it would be good as a review, remediation or scaffolding.