# Thread: SA of a regular tetrahedron

1. ## SA of a regular tetrahedron

A regular tetrahedron is a triangular
pyramid. What is the total surface
area of a regular tetrahedron with
base edges of 7 cm?

I started by using
1/2 × Perimeter × [Side Length] + [Base Area]
(1/2) (21) (?) + (sqrt(36.75))

So im not sure if this is the correct forumula or if the numbers i used to plug in are correct.

2. The tetrahedron has four faces, each of which is an equilateral triangle with sides 7 cm. So your answer should be 4 times the area of that triangle.

The area of the triangle is half the base, times the vertical height which in this case is $7\sin60^\circ = 7\sqrt3/2$.

Put all that information together and you'll get the answer.