Study of asymptotes in Calculus in mathematics textbooks for general upper secondary education in Croatia

Asymptotes in the upper secondary mathematics curriculum are related to graphs and limits of elementary functions. We analyzed fourth-grade mathematics textbooks for general upper secondary education in Croatia concerning the study of asymptotes in Calculus. Asymptotes occurred in several praxeologies confined to two units ; one related to function limit and the other to applying derivatives in function graphing. The study of asymptotes was organized around two didactic moments: the institutionalization of formulas and working on determining asymptotes. We propose exploring the asymptotic behaviour of a function to motivate the construction of formulas with a limit for the coefficients of slant asymptote and generalized asymptotic relations.