Sum of the Interior Angles in a Pentagon

① This example dynamically demonstrates that the sum of interior angles in a pentagon is always 540°. ② The core mathematical concept is the polygon interior angle sum formula (n-2)×180°, along with the triangulation method—dividing the pentagon into three triangles to derive the total. ③ Construction highlights: using GeoGebra's Segment command to connect vertices A, B, C, D, E forming the pentagon, and Point command to create auxiliary points (e.g., E₁) that support internal diagonals (k, i, l) for triangulation; objects include segments f, g, h, a, b, j and points F, G for labeling and interaction. ④ Suitable for middle school geometry lessons or high school review, ideal for classroom demonstration, student exploration of the angle sum formula, or as a dynamic worksheet resource.