Double Reflections Across Intersecting Lines

This example demonstrates a double mirror reflection across two intersecting lines, showing how a figure's position and orientation change after two successive reflections. Core mathematical concepts include geometric transformations (reflection), angle preservation, and congruence of polygons. Construction highlights: points and intersecting lines are created with Point and Line; an initial polygon is built with Polygon; the Mirror command reflects the polygon's vertices sequentially across the two lines; Angle and Segment commands annotate the reflection angles and corresponding segments; key objects include h, N, M, a, O, b, A, B, C, poly1 and their reflected counterparts A', B', C', poly1', etc. Suitable for middle‑school geometry transformation lessons, high‑school analytic geometry review, and as an introductory GeoGebra transformation demo.