The use of GeoGebra to explore the solution
Jessica used GeoGebra to simulate the construction of the rectangular lawn and the
triangular flowerbed (Figure 5), but the text that she sent
allows a clear understanding of her reasoning. She recognized
that the area of the triangular flowerbed equals the value
chosen for the length of the rectangle. However, this
conclusion arose from the manipulation of the variable
"height" of each of the coloured triangles:
The yellow triangle is divided by the 2m stick in two triangles.
The base of each triangle measures 2m – the length of the stick.
To determine the area of a triangle, we have to calculate: height
× base/2. In order to measure the area of those two triangles, we
have: height × 2/2. But it is clear that 2/2=1, so the area of these
triangles equals their height.
Although Jessica’s construction satisfies the three conditions, similarly to the previous
solutions, it reveals distinct features in terms of manipulation. Such differences show
that Jessica’s thinking process is also distinctive: the absence of measurements or
calculations stands out, the construction of a slider allows changing the stick’s size;
and moving the free point on the right side changes the size of the rectangle.
This file reveals Jessica’s mathematical and technological fluency in that the
GeoGebra construction is built under the perspective of geometrical properties and
relations, rather than aiming at measuring or calculating. The quantitative relationship
that she explains appears embedded in a geometric representation which is very
powerful since it invites at manipulating and therefore generalizing. Adding a slider
that controls the length of the stick involves analysing a variable that is not explicit in
the statement of the problem; hence Jessica’s exploration goes far beyond what was
requested to solve the problem.