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?

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  1. 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

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  2. Thanks, but I need the base too - that I can do by myself!

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