General Quadrilateral with Diagonals

This GeoGebra example demonstrates the geometric construction of a general quadrilateral and its two diagonals. By defining four points A, B, C, D in the plane and connecting them, we explore the fundamental properties of quadrilaterals. Key mathematical concepts include quadrilateral classification, diagonal intersection, and angle measurement. Construction details: Use the Segment command to draw the four sides AB, BC, CD, DA; use the Intersect command to find the intersection point E of the two diagonals; use the Angle command to measure the interior angles α, β, γ, δ at each vertex and the angle ε between the diagonals. Suitable for middle school mathematics students learning about polygons and geometric construction, as well as a foundation for high school coordinate geometry.