Resumen
Errors are a major component of the pedagogical content knowledge (PCK) needed for teaching mathematics. In this study, 25 prospective teachers (PTs) in high schools were invited to solve a trigonometric task that had been assigned to high-school students and, subsequently, to relate to an authentic solution containing mathematical errors, which was presented in a dialogue by a pair of students. While all PTs reached the final, correct solution, eight provided only one of the two results in one step of the solution. Almost all (23) PTs identified at least one of the students? errors. The case raised issues regarding the steps that should be written in a solution and the role of drawings in mathematical problems. This article suggests that exposing PTs to authentic teaching cases provides opportunities to discuss subtle issues related to their own mathematical knowledge and to obstacles that their future students might encounter when solving such tasks.