The teaching of optimization, has usually become a mechanical process and devoid of arguments: in general their uses are ignored in specific situations of other disciplines, such as engineering. With the Socio - Epistemological Theory, we make an empirical investigation, where the epistemology of uses is problematized to value the functional justification demanded by other domains of knowledge. We analyze aspects of the Lagrange Analytical Mechanics work and the work of mechatronic engineers. Engineers in training were defined as the study community and the emergence of a specific selection situation is supported as its uses and meanings of optimization. The methodology consisted in the technique of documentary analysis and semi-structured interviews. It was found that selection situations generate optimization meanings and arguments.