APOS theory in learning mathematics (using trigonometry as an example)

Introduction. One of the most well-known theories that allows us to study the process of structuring a concept in the mind of a student is the APOS theory, specially created for the study of mental processes in mathematical education and worthy of application in other disciplines. Despite numerous studies on methods of teaching mathematics, in recent years there have been few publications on the problem of students' understanding of mathematical concepts; there are practically no works devoted to the study of the formation of mental structures in the course of students' assimilation of mathematical concepts. The aim of the article is to analyze the process of mastering mathematical concepts using the example of trigonometric functions and present the results of the study in accordance with the stages of the APOS theory.