“…Other studies reveal the limitations in the knowledge of the content, such as the recognition of the different mathematical meanings of the equal sign (e.g., [60]); solving algebraic tasks mainly by trial and error, not paying attention to the structure of the problem and the knowledge involved in developing algebraic thinking (e.g., [64]); difficulties solving problems involving the generalization of patterns related to the discrimination of strategies in the use of proportionality, explanation of a growth pattern and obtaining a general rule (e.g., [66,68]); ignorance of the central issues that the characterization of and working with algebraic thinking imply, such as solving mathematical problems that require the representation of unknown quantities (e.g., [56]) and the case of the generalization of arithmetic with the properties of numbers, the operations and the meaning of the equal sign as equivalence (e.g., [65]); and a lack of strategies for generalizing functional relationships, and problems understanding and connecting the different representations of functions (e.g., [71]).…”