math/geometry

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What are the surface areas of this two figures?
a) a triangular pyramid with base of 5 cm, an altitude of the base of 8.7 cm and a slant height = 6.9 cm
b) a square pyramid with a slant height of 5.2cm and an altitude of the triangle of 9cm.

  • math/geometry -

    Surface area of any pyramid is base area+ 1/2 slantheight*perimeter.

    a) To get base area, we use Heron's formula
    Area= sqrt(s(s-a)(s-b)(s-c))
    where s is one half perimeter or
    Base Area= sqrt(7.5*2.5)^3)=you do it.
    Slant height= sqrt (6.9^2 + (.5*8.7)^2)
    Perimeter=15

    b) I don't see how the altitude can be greater than the slant height.

  • math/geometry -

    got it!

  • math/geometry -

    I assume you caught my typo...
    base area=sqrt(7.5(2.5)^3)

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