Interactive Verification of Polygon Interior Angle Sum

This GeoGebra example uses a variable-sided polygon to visually demonstrate how the interior angle sum changes with the number of sides, allowing students to compare constructed angle measures with the theoretical result. It centers on the mathematics of polygon interior angles and the formula (n−2)·180° for an n-gon, supported by angle measurement, summation, and a triangulation (divide-into-triangles) reasoning. Construction-wise, it leverages GeoGebra commands and objects such as Sequence to generate indexed data for the polygon configuration, and Polygon to build the polygon itself. It then organizes sides/vertex indices (e.g., lists like sidelist) and computes each interior angle, collecting them into angle lists (via intermediate list objects) before summing them (represented by a total like sang). Text/label objects are used to mark vertices for clarity. Suitable for middle school to early high school learners and for classroom exploration, dynamic geometry verification, and strengthening understanding of the general interior-angle-sum rule.