Question

A pyramid has all sides that are equilateral triangles. Each triangle has side lengths of 9 centimeters. If the surface area of the pyramid is 140.4 square centimeters, what is the slant height of the pyramid?

Answer 1

So for the surface area (SA) of the pyramid,
SA = 4×1/2×b×h, base (b) is side length and h is the unknown slant height. shortened is:
SA = 2bh
140.4 = 2×9 h
140.4 = 18h
h = 140.4/18 = 7.8 cm

**there's another shorter way to handle equilateral triangles, if you've learned the secret to a 30-60-90 right triangle ;)