Posted by Fustrated on .
The base of a regular pyramid is a square whose sides have a length 8 cm. If a lateral edge of this pyramid has length 20 cm, what is the surface area of the pyramid?

math 
Reiny,
Look at one of the triangles, which is isosceles with a base of 8 and each of the equal sides of length 20
Height of triangle: let it be h
h^2 + 4^2 = 20^2
h^2 = 384
h = √384
Area of one triangle = (1/2)(8)(√384) = 4√384
Assuming the surface area consists only of the 4 triangles,
surface area = 4(4√384) or 16(8√6) = 128√6 
math 
Fustrated,
Thanks, but I need the base too  that I can do by myself!