Using GeoGebra to obtain the solution
Marta and Miguel submitted their solution along with a GeoGebra file (Figure 2). They
represented the rectangular lawn as well as the three conditions of the statement: a stick
with length 2 (segment FG) is perpendicular to the
side AD of the rectangle, and the “rope” (segment
JI) passes through the end of the stick, intersecting
it at point G. Next, they determined the areas of
two triangles, obtained by dividing the triangle FJI
through the stick (segment FG). By dragging F
they verified that the total area did not change and
therefore they concluded that Rose was right.
This solution reveals Marta and Miguel’s
technological fluency, particularly when handling
GeoGebra: they perform constructions that strictly meet the initial conditions and
determine areas using the measuring tools. As to their mathematical fluency, and
analysing the construction protocol, they seem to be familiar with geometrical
concepts such as “perpendicular line” and “parallel line”, “polygon” and “area of a
polygon”. Nevertheless, they fail to submit a mathematical reason for the invariance of
the areas, which may result from the “certainty” they seem to get from dragging F.