We present some results from a research study in which five mathematics teachers worked on a functional graphic approach to solve inequalities. We developed activities using algebraic, graphic and natural language registers (Duval, 1995, 2000) in order to engage teachers in the solution treatment within different registers and in conversions between them so they might become aware of the errors they make when using algebraic methods in the light of comparisons with graphical methods. Analyses of teachers’ protocols were undertaken to identify formal, intuitive and algorithmic aspects (Fischbein, 1993). Our findings showed that teachers did not search for mathematical reasons as why their algebraic and graphical strategies resulted in different solutions, suggesting that they had not fully appropriated the formal aspects of the algebraic solving methods they normally use to solve inequations.
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