Circle Theorem 1: Inscribed Angle Demonstration

① This example demonstrates the Inscribed Angle Theorem: angles subtended by the same arc in a circle are equal. ② Core mathematical concepts include circles, inscribed angles, arcs, angle relationships, and basic geometric construction. ③ Construction highlights: GeoGebra commands Circle (creates circle c), Point (places points A, B, C, D, E), Polygon (forms polygon poly1), Angle (measures angles α, β); objects involved are circle c, points A‑E, polygon poly1, segments a, c_1, d, e, and angle markers α, β. ④ Suitable for middle‑school geometry (grades 7‑9) and high‑school review of circle theorems, useful for classroom demonstration, self‑study, or flipped‑classroom material.