Exterior Angle of a Triangle – Dynamic Demonstration

① This GeoGebra example dynamically demonstrates the exterior angle theorem of a triangle, showing that an exterior angle equals the sum of the two non-adjacent interior angles. ② Core mathematical concepts include the definition of interior and exterior angles, angle measurement, and the relationship between angles in a triangle. ③ Construction details: The triangle poly1 is created using the Polygon command with vertices A, B, C; a ray is drawn from vertex C extending side BC to form the exterior angle; the Angle command marks interior angles α, β, γ and exterior angles δ, ε, ζ, with text objects text1, text2, text3 displaying their measures for real-time comparison. ④ Suitable for middle school geometry lessons, teacher demonstrations, or student self-exploration to visually verify the theorem and deepen understanding of angle relationships.