This demonstration of Heron's formula is straightforward and elementary. Working through it with students can provide fruitful ideas of strategy, symmetry, planning, and observation. We now switch to consider some problems and investigations for which Heron's formula is useful.
Problem:
Show that the maximum area of a triangular region with a fixed perimeter occurs for an equilateral triangle.
Comment. I would adapt the statement and context of this problem depending on the background of the students. Above, I mentioned an exploratory investigation where students looked at different triangular regions that could be formed with a perimeter of 100 feet. Now extend this. Have students organize a table where the lengths of the sides are varied systematically .
In order to vary something "systematically" one needs to identify a variable that can be ordered in the table. For example, investigate the more manageable problem of isosceles triangles. Let the side of length a be the base to vary from 2 to 48 in steps of 2, as follows