Reflecting a Triangle

① This example demonstrates how to reflect a triangle across a line (the axis of reflection), producing a mirror image that is congruent to the original triangle. ② Core mathematical concepts include geometric reflection (axial symmetry), coordinate geometry, congruence, and the invariance of angles and distances under reflection. ③ Construction highlights: using GeoGebra commands such as Polygon to create triangle ABC, Line to define the reflection axis, and then reflecting points to obtain D, E, F which form the reflected triangle; objects involved include points A, B, C, D, E, F, lines t1, c, a, b, and polygons. ④ Suitable for middle school geometry lessons or introductory high school coordinate geometry, helping students intuitively grasp the properties of axial symmetry and precise construction using digital tools.