Quadrilateral and Its Interior Angles

This example demonstrates an arbitrary quadrilateral defined by four vertices A, B, C, D, with its four interior angles α, β, γ, δ clearly marked. The core mathematical concepts involve basic properties of polygons and angles in plane geometry, including the fact that the sum of interior angles of a quadrilateral is 360° and the measurement of each vertex angle. Construction details: using GeoGebra's Segment command to connect the vertices and form the four sides f, g, h, i, and the Angle command to label each interior angle, providing a clear visual representation of the quadrilateral's structure. This is suitable for middle school geometry lessons, helping students recognize the basic elements of quadrilaterals, understand interior angles, and serve as a foundation for exploring polygon angle-sum theorems or dynamic geometry investigations.