Using Cabri 3D diagrams for teaching geometry

Cabri3D is a potentially very useful software for learning and teaching 3D geometry. The dynamic nature of the digital diagrams produced with it provides a useful aid for helping students to better develop concept images of geometric concepts. However, since any Cabri3D diagram represents three-dimensional objects on the two dimensional screen of a computer, some care is needed in order to avoid serious misconceptions which can arise from its use, in particular those due to the fact that projections do not preserve, in general, angles and distances. In this paper, after comparing digital diagrams (i.e. diagrams on a computer screen) with the more usual diagrams and models, we illustrate an experience around the use of Cabri3D with prospective high school teachers, aimed at clarifying which misconceptions may arise while interpreting a Cabri3D diagram.