Conceptualising the regular pentagon in collaborative argumentation

International audience ; This case study examines a group of Hungarian mathematics pre-service teachers solving an open problem collaboratively, where they must determine whether a folded shape is a regular pentagon. The study looks at how different factors, such as using perceptual evidence, ostensive arguments, and mathematical arguments, impact proof development. The study draws from theories such as Cognitive unity and the van Hiele model to analyse the students' argumentation. The video recording of the session was used to collect data. The results showed that students' argumentation had a strong dynamic between perceptual and mathematical character; moreover, the conceptualisation of the regular pentagon evolved as they advanced in the construction of their proof.