The technique to solve equations of the first degree. A case study

In Mexico we can find upper secondary teachers who, sometimes, are forced to teach mathematics even though their profile is different. This document is aimed to identify the technique –mathematical methods– that a teacher from the Mexican Telebachillerato subsystem (high school) uses to help students to solve the type of tasks related to first-degree equations. This proposal is part of a research project where thirteen teachers participated, and who allowed to be observed twice teaching mathematical contents according to their study program. The purpose of observation works was to make them a discussion object with the participants. This is a study case research. The results show that the teacher creates a technique focused on obtaining determinants to solve types of task about system of equations, but the theory which proves its functionality is reduced to a more didactic than mathematical discourse. In the classroom, techniques to solve problems are taught, but these remain unprotected from mathematical theories (mathematical argument) that can validate their functionality, the student is the one who has to infer o build his own theory from the teacher’s technique.