Géométrie, graphiques, fonctions au collège

mathematical learning is a long term process that occurs, usually, in an institutional structure: the school. the student builds his knowledge over the years, in an interactive relationship with his teachers, other students in his class and all the other sources that social life makes available. in this text, we present a set of problems where the mathematical subject is the notion of approximation. it is treated at a time of the syllabus: 12-15-year-old students, in a contextualized way. it is only an approach; the question of the error calculation is not addressed. numbers and measures are there involved in the different frameworks in interaction: numerical, geometric, functional, and graphic. there, we explain our didactic choices and the reasons for the election of the engineering proposed. the reference is the tool-object dialectic and the frameworks interplay. it offers us a table to elaborate the sequences of class, and also to report and analyze the relations between teacher and students: who is responsible for what, who does what. the teacher has leeway to organize and lead his teaching; he has his expectations concerning students. we make reference here.