Analogy and dynamic geometry system used to introduce three-dimensional geometry

We present a sequence of classroom activities on Euclidean geometry, both plane and space geometry, used to make three dimensional geometry more catchy and simple. The activity consists of a guided research activity that leads the students to discover unexpected properties of two apparently distant geometrical entities, quadrilaterals and tetrahedra. The activity has been realised by means of an efficacious conceptual tool, the analogy, and an operative one, a dynamic geometry system.