Why do this problem
encourages learners to consider familiar mathematical ideas in less less familar contexts. The problem will make connections with triangluar numbers and Pythagoras' theorem. If non-standard units of area (equilateral triangles) are used calculation can be made easier.
Draw the two triangles and ask the group to consider how they would calculate their areas. Share ideas. If the suggestion does not arise from the group - draw one of the triangles on an isometric grid and ask the question again, seeking to draw attention to areas using areas of triangles as the unit of measurement.
Now pose the problem and leave the group to experiment, raise and test conjectures.
What about triangles whose sides are not of integer length?
Find a rule for the areas of all equilateral triangles with a side of integer length. Can they use this to generate some examples?
Do the findings work when using areas measured in square units?