The plan proposes a succession of tasks exploiting the potential a priori offered by Casyopee for approaching and studying the notion of function, and especially:

- the role played by functions for solving problems arising from geometrical situations,

- the role played by parameters for studying family of functions and accessing generalization.

Specific importance is given to the construction of tasks where students can choose different variables for exploring functional dependencies and to the connection between algebra and geometry. This connection is supported in Casyopee by geometric expressions which allow to express magnitudes in a symbolic language mixing geometry and algebra. Moreover, according to the choices made for the independent variable, the resulting algebraic expression of functional dependence automatically produced by Casyopee can be of very different complexity. The scenario aims at exploiting these didactical functionalities of Casyopee and the different associated feedbacks, coherently with the theory of didactic situations.

The instrumentalisation process is initiated in each phase of the scenario through a collective phase orchestrated by the teacher, which also serves as a devolution phase for the type of task which is considered.

The scenario is built around three main types of tasks :

- finding targetted second grade functions by acting on parameters (five different tasks according to the semiotic forms used for these functions),

- functional modelling of a geometrical situation for solving a problem of relationships between areas,

-functional modelling of a geometrical situation for solving an optimization problem.