Visualizing the Angle Sum Property of Quadrilaterals

This example constructs a general quadrilateral in the plane and labels its four interior angles to visually demonstrate the invariant property that the sum of interior angles of any quadrilateral is always 360°. It focuses on the key geometry concepts of interior angles, angle measurement, and reasoning with sums of angles that remain constant even as the quadrilateral shape changes. In GeoGebra, the construction uses the Polygon command to create the quadrilateral from points A, B, C, and D, and the Angle command to measure and display the four interior angles (α, β, γ, δ) together with supporting angle-related objects such as q1 and a, b, c, d. Text objects (text1–text4) are used to present the measured angle values and the final angle-sum statement. Suitable for middle school geometry instruction, exploratory learning with dynamic geometry, and revision of quadrilateral angle properties.