# math/geometry

posted by .

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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