Quadrilateral Reflection Line: Mirror Symmetry Construction

① This example demonstrates how to construct a line of reflection for an arbitrary quadrilateral and generate its mirror image across that line. ② The core mathematical concept is axial symmetry (reflection) in plane geometry, involving the axis of symmetry, corresponding points, corresponding sides, and congruence of figures. ③ Construction details: Using GeoGebra commands such as Polygon to create quadrilateral poly1, Midpoint and Segment to construct midpoints and segments, Line to define the reflection line, and Mirror to reflect the quadrilateral and its sides, producing the mirrored polygon poly1' and corresponding edges a'_1, etc., while retaining both original and reflected objects. ④ Suitable for middle school geometry or introductory high school analytic geometry, helping students intuitively understand reflection transformations and explore how the position of the symmetry axis affects the resulting figure.