3.1 Preliminary remark
The observation has been made through an open question questionnaire having the following purpose:
· In the first question the student are invited to say if what they see is a triangle and why. This helps them to
think about characteristic of a triangle and obtain an implicit model towards the triangle.
· The second question asks the pupil to draw a triangle and define it by words. The drawing they have made
corresponds to their mental picture of the geometrical figure.
· The third and fourth questions are aimed at discovering if pupils understand the relation among sides and
among angles of the figure and which strategies they adopt in choosing the measures.
· The last question is aimed at putting in evidence the concept of the height they have gained and
misconceptions which hamper the comprehension of height in a given triangle.