Covariation in Precalculus Textbooks Tasks: a Case of Trigonometric Ratios

Abstract Variation learning has been recommended in several academic curricula around the world; however, the manner in which university textbooks carry out this purpose is unclear. We carried out an analysis of the textbook tasks in order to identify the way in which covariation is present in the trigonometry tasks. Content analysis tools were used to analyze the tasks of five university precalculus textbooks. The study shows a special emphasis on tasks that miss opportunities to mathematize the covariation. This article offers a typology of tasks and also suggests the possibility of reorganizing some of them, in order to promote covariation studies.