Pearson Geometry Common Core, 2011
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Pearson Geometry Common Core, 2011 View details
3. Surface Areas of Pyramids and Cones
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Exercise 28 Page 714

Use the formula for the surface area of a prism and for the surface area of a pyramid.

About 45 square meters

Practice makes perfect

We will find the surface area of the following composite solid.

The solid consists of two parts.

  • A right rectangular prism that is 2*2*4 meters.
  • A regular square pyramid with the height of 2 meters and a base edge of 2 meters.
To find the surface area of the composite solid we will find surfaces areas from the prism and from the pyramid, then add them together.

Surface Area of the Pyramid

Only the lateral area of the pyramid is part of the surface area of the composite solid. The lateral area of a right pyramid is given by the following formula. L.A.=1/2Pl Here, P is the perimeter of the base and l is the slant height of the pyramid. Since the base is a square with an edge of 2 meters, its perimeter is P=4* 2=8 meters. Now, let's find the slant height, l.

Segment AB is half of the base edge of the pyramid. Therefore, AB= 22=1 meter. Now, let's use the Pythagorean Theorem for right triangle △ ABC.
AB^2+ AC^2= BC^2
1^2+ 2^2= l^2
Solve for l
1+4=l^2
5=l^2
l^2=5
l=sqrt(5)
l=2.236067...
l≈ 2.24
Now, let's find the lateral area of the pyramid.
L.A.=1/2Pl
Substitute values and evaluate
L.A.=1/2( 8)( 2.24)
L.A.=1/2* 17.92
L.A.=17.92/2
L.A.=8.96
The surface area from the part of the pyramid is about 8.96 square meters.

Surface Area of the Prism

The lateral area of the prism and one base area is part of the surface area of the given composite solid. The lateral area of a right prism is L.A.=Ph, where P is the perimeter of the base and h is the height of the prism. L.A.=Ph Since the base is a square with a base edge of 2 meters, its perimeter is P=4* 2=8 square meters. Therefore, L.A.=8* 4=32 m^2. Since the base is a square with base edge 2 m, its area is B=2^2=4 m^2. Therefore, the part of the surface area of the composite solid from the prism is 32+4=36 square meters.

Surface Area of Composite Solid

Now, let's add the partial surface areas and round it to the nearest whole number to find the answer. S.A. & =8.96+36 & = 44.96 ≈ 45 This tells us that the surface area of the given solid is about 45 square meters.