Posted by **katie** on Tuesday, November 11, 2008 at 10:21am.

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 -
**bobpursley**, Tuesday, November 11, 2008 at 10:38am
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 dont see how the altitude can be greater than the slant height.

- math/geometry -
**katie**, Tuesday, November 11, 2008 at 11:06am
got it!

- math/geometry -
**bobpursley**, Tuesday, November 11, 2008 at 11:59am
I assume you caught my typo...

base area=sqrt(7.5(2.5)^3)

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