Triangles: Definition and Elements

① This GeoGebra example dynamically illustrates the definition of a triangle and its basic elements (vertices, sides, interior angles), helping learners intuitively grasp the fundamental structure of triangles. ② Core mathematical concepts include the definition of a triangle (a closed figure formed by three line segments), vertices, sides, interior angles, the sum of interior angles being 180°, along with introductory ideas of circumcircle and tangent lines. ③ Construction highlights: the Polygon command creates triangle pol1, the Angle command marks interior angles α, β, γ, and text objects texto1, texto2, texto4 label vertices and sides; points A, B, C are vertices, a, b, c are side lengths, and c also denotes the circumcircle. ④ Suitable for middle school geometry introduction, high school review of triangle properties, or as a basic GeoGebra construction demonstration. Dragging vertices allows dynamic observation of shape changes, deepening understanding of relationships among elements.