The objective of this research was to characterize the pedagogical content knowledge put into play in the design of a plan for teaching location in the Cartesian plane. For this purpose, the theoretical model Mathematics Teacher's Specialized Knowledge (MTSK) was used as an analytical tool to study the knowledge mobilized by the teacher. The methodology was qualitative through an instrumental case study with a Colombian teacher. The information was collected through the design of a lesson plan

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... nd a semi-structured interview. As a result of the analysis, descriptors were obtained that theoretically grounded the knowledge mobilized by the teacher. The lesson plan was shown to be a favorable scenario for studying the teacher's didactic knowledge used in the teaching of mathematics. The fact of knowing different teaching strategies, students' expectations and interests, and possessing knowledge of the mathematical competences to be developed, allows the teacher's didactic contributions to be seen as additional knowledge to mathematical knowledge.