Resumen

We propose the a priori analysis of an activity involving geometry, arithmetic and numerical representations of rational numbers. It starts with a geometric manipulation with GeoGebra and gradually leads students to consider the divisors of 360 and to reflect upon approximations and exact representations of angle measurements. A first ‘off-class’ experiment is presented and discussed, as a case study. Through it, we acknowledge that it is possible to design suitable teaching situations, so as to make students reflect in a meaningful context on the dualities ideal object / visual representation, exact measurements / approximations, and on the type of certainty intended from a mathematical standpoint. The activity takes place in the ‘geometer-physicist’ paradigm proposed by Tanguay & Geeraerts (2012, 2013) and instilled by Jahnke (2007, 2010).