Use this applet for class demonstration or for student self directed learning.
Other useful applets for checking on irregular polygons
Interior Angles :
https://www.geogebra.org/material/show/id/7100 (Angles already displayed, to sum up)
https://www.geogebra.org/material/show/id/26422 (Construct own triangles by joining vertices, discover formula for sum)
Exterior Angles :
https://www.geogebra.org/material/show/id/26430 (Angles already displayed, to sum up)
https://www.geogebra.org/material/show/id/36302 (Move slider to see visual impact of sum of exterior angles in polygon)
Footnote :
Geogebra Team's applet at https://www.geogebra.org/material/show/id/8915 published in 3 May 2012
was derived from my work prior to 14 Aug 2011 at http://tinyurl.com/dmnggbregpolygon
Due to Geogebra version updates, the file in 2012 used is not displaying correctly.
I consulted on forum and found some changes to Sequence command which cause display problem so I have updated the display.
