Interest for the use of graphics calculators has guided the group « Analysis » of the IREM of Montpellier to propose activities in which this equipment is used. As an example it has been provided for the pupils – during hours of « independant study » on secondary level – the problem of determining a parabola touched tangential by three given straight lines, which corresponds – from the teachers viewpoint – to the problem of finding out the role of coefficients, a, b, c in a trinomial term ax^2+bx+c. The most important element of a first session has been an experiment and a (nearly free) research of the problem from the pupils’ side with help of a calculator, as well as an intensive exchange of ideas between the pupils and the teacher, but also among themselves. As a result of this experience the author finds out that activities of the kind « independent study » can not be renounced of, particularly in mathematics. The pupils can drive away false thoughts, discover their erroneous character by making them work as an obstacle in the solution of a problem. Nevertheless, the activity as such is no pledge for learning. That is, above all, as even a working activity can be penetrated by a lot of erroneous ideas. (ZDM/Mathdi)