Surface Area of a Pyramid

## Surface Area of a Pyramid

The formula for the surface area of a pyramid is based on three items: the length of the slope on each face; the area of each face; and the area of the base.

The slope length of each face is calculated using Pythagoras Theorem: the slope length for one face is

s = sqrt(h^2 + (frac(1)(2)l)^2)

and similarly for the other three faces. Note that the base of the triangle is either frac(1)(2)l or frac(1)(2)w.

If the pyramid is based on a square or rectangle then congruent faces will have the same slope length.

From the sloping length, calculate the area of each triangular face:

text(Area) = frac(1)(2)ws or text(Area) = frac(1)(2)wl

Finally calculate the area of the base text(Area) = lw.

Add the areas for the four parts together.

## Example 1

A structure has been built in the shape of a right square pyramid. The vertical height is 6m, and the length of each side is 6m at its base. To the nearest whole metre, what is the surface area off the entire structure?

 Centre to side (b) b = frac(1)(2) xx 6 = 3 Slope length (c) c = sqrt(a^2 + b^2) = sqrt(6^2 + 3^2) = 6.708 Area of face Aface = frac(1)(2)(6)(6.708) = 20.125 Area of base Abase = wl = (6)(6) = 36 Total Area A = 4Aface + Abase = 4(20.125) + 36 = 116.498

## Example 2

A shape for an engineering component has been manufactured as a pyramid.

What is the surface area of the sloping sides of the pyramid, which has a base of 9cm by 6cm and a vertical height of 4cm?

 Slope lengths s1 = sqrt(3^2 + 4^2) = 5 s2 = sqrt(4.5^2 + 4^2) = 6.021
 Area of Sides A1 = frac(1)(2)(9)(5) = 22.5 A2 = frac(1)(2)(6.021)(6) = 18.063 TOTAL Area = 2A_1 + 2_A2 TOTAL Area = 2(22.5) + 2(18.063) = 81.126`