In mathematics textbooks triangles used investigation in the context of prototypicity

One of the best ways to understand and teach mathematical abstract concepts is to use concrete examples from daily life and that come to mind first. The examples that first come to mind and facilitate learning are called prototypical examples. While prototypical examples can facilitate learning in the first stage of learning, they might cause mathematical misconceptions if used too frequently. The aim of this study is to examine triangle examples in the mathematics textbooks taught from 1st grade to 12th grade in schools affiliated with the Ministry of National Education in the 2022-2023 academic year, in the context of prototypicality. The scope of the research consists of a total of 28 mathematics textbooks, 8 at the primary school level, 8 at the secondary school level and 12 at the high school level, approved by the Board of Education and Discipline. The data of the current research was obtained through document analysis, which is one of the qualitative research methods. The "Prototypic Triangle Detection Form" developed by the researcher was used as the data collection tool in the study. The obtained data were calculated as frequencies and percentages and presented in the form tables. According to the data obtained, although it was seen that the use of prototypical examples decreased as the grade level progressed in primary, secondary and high school levels, it was determined that the rates of prototypical example usage were very close to each other at the grade levels. However, it was determined that the use of prototypical triangles in mathematics textbooks was more prevalent than the use of non-prototypical triangles, and that there were no examples of non-prototypical triangles in 7 mathematics textbooks. Various recommendations were proposed based on the obtained findings and data analysis. Key Words: Prototypical Examples, Prototype, Mathematics Textbook, Geometric Shapes, Triangles