Sum of Angles of Quadrilateral

This GeoGebra example dynamically demonstrates that the sum of the four interior angles of any quadrilateral (including rectangles, rhombi, squares, trapezoids, and kites) is always 360°. The core mathematical concept is the polygon angle-sum formula (n-2)×180°, which for n=4 gives 360°, along with angle measurement, rotation, and angle rearrangement. The construction uses the Polygon command to create quadrilateral poly1, the Angle command to mark interior angles α, β, γ, δ, and the Rotate command to bring all angles to a common vertex G, supported by Segment, Circle, and Textfield for interactive input. Users can drag vertices to see the angle sum remain constant. Suitable for middle school geometry lessons to verify the quadrilateral angle-sum theorem and explore angle properties of special quadrilaterals.