At that point, the students realised that to find the area of the triangular faces, what they really needed was the height of the triangular face (the slant height of the pyramid, l, and not the height of the pyramid, h).
This strategy did not work because the slant height l needed to be expressed in terms of h, the height of the pyramid.
As the students engaged in class discussion and reflection, one student remarked that the lateral surface was a sector of another circle with radius equal to the slant height l, of the cone (note that l = [square root of [r.sup.2] + [h.sup.2]]) and that they could use l to construct a circle with a sector equivalent to the lateral surface of the cone.
* We know the height of the cone, h, and its slant height, l.
* Using points A and C, construct the slant height of the cone.
* Measure the circumference of c1 and the slant height AC.