Definition of a Trapezoid

This GeoGebra example dynamically illustrates the definition of a trapezoid, showing a quadrilateral with one pair of parallel sides and the other pair non-parallel. The core mathematical concept is the criterion for identifying a trapezoid, involving parallel lines, segments, vertices, and basic quadrilateral properties, with extensions to isosceles and right trapezoids. Construction highlights: the Segment command creates the sides, the Line command constructs parallel lines, and the Point command marks vertices A, B, C, D, while auxiliary lines f, g, h, i, j verify the parallel relationships; dragging vertices reveals how the shape changes. This is suitable for middle school geometry lessons or self-study, helping students intuitively grasp the trapezoid definition and distinguish it from parallelograms and rectangles.