Opposite Angles of Parallelograms Are Congruent

①This GeoGebra example dynamically demonstrates that opposite angles of a parallelogram are congruent, a fundamental property in Euclidean geometry.②Core mathematical concepts include the definition of a parallelogram, parallel opposite sides, the theorem of congruent opposite angles, rotation and congruence transformations, and angle measurement.③Construction highlights: using the Polygon command to create parallelogram poly1, Midpoint to find the intersection M of diagonals, Rotate to rotate the entire figure by 180° producing congruent parallelogram poly1', and Line, Segment, Angle commands to label sides and angles; text objects text1, text2, text3 display the angle measures α, β, γ, δ for direct comparison.④Suitable for middle school geometry lessons or introductory high school vector/plane geometry, this interactive tool supports classroom demonstration, student exploration, and verification of geometric theorems, reinforcing the role of rotation in proving congruence.