Alternate Angles Interactive Demonstration

① This GeoGebra example dynamically demonstrates the equality of alternate interior angles formed when two lines are intersected by a transversal. ② The core mathematical concept is the alternate angles theorem in parallel line geometry: when two parallel lines are cut by a transversal, alternate interior angles (such as α and γ, β and δ) are congruent. The example also involves angle measurement, congruence, and geometric construction. ③ Construction details: Based on the summary, the commands used include Line, Midpoint, Point, and Angle, creating lines a, c, b and points A, B, C, D, E, F, with four labeled angles α, β, γ, δ. Midpoints and points help visualize the angle relationships. ④ This is suitable for middle school geometry (grades 7–8) when teaching properties of parallel lines and transversals, and can be used by teachers for classroom demonstration or by students for self-exploration to distinguish alternate, corresponding, and same-side interior angles, enhancing spatial reasoning and logical proof skills.