Geometry
Chapter 1
Topics: Space Figures, Volume, and Surface Area 9-5-2 Š 2008 Pearson Addison-Wesley. All rights reserved
Space Figures, Volume, and Surface Area • Space Figures • Volume and Surface Area of Space Figures
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Space Figures Space figures take three dimensions of space to represent the figure. One important group of space figures is a group called polyhedra. The faces of these figures are made only of polygons.
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Regular Polyhedra (Platonic Solids) Name
Description
Tetrahedron
4 equilateral triangles
Hexahedron
6 squares (cube)
Octahedron
Groups of 4 regular triangles
Dodecahedron
Groups of 3 regular pentagons
Icosahedron
Groups of 5 regular triangles
See pictures on the next slide. 9-5-5 Š 2008 Pearson Addison-Wesley. All rights reserved
Space Figures
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Space Figures The next slide shows space includes two other polyhedra: pyramids and prisms. Pyramids are made of triangular sides and a polygonal base. Prisms have two faces in parallel planes; these faces are congruent polygons. The next slide also shows a torus which is a doughnut-shaped solid and figures made up in part of circles including right circular cones and right circular cylinders. 9-5-7 Š 2008 Pearson Addison-Wesley. All rights reserved
Space Figures
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Volume and Surface Area Volume is a measure of capacity of a space figure. Volume is measured in cubic units. Surface Area is the total area that would be covered if the space figure were “peeled” and the peel laid flat. Surface area is measured in square units. 9-5-9 © 2008 Pearson Addison-Wesley. All rights reserved
Volume of Surface Area of a Box The volume V and surface area S of a box with length l, width w, and height h is given by the formulas
V = lwh and S = 2lw + 2lh + 2hw. h l
w 9-5-10
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Example: Volume of Surface Area of a Box Find the volume and surface area of the box below. 3 in. 7 in.
Solution
2 in.
3
V = 7(2)(3) = 42 in.
2
S = 2(7)(2) + 2(7)(3) + 2(3)(2) = 82 in.
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Volume of Surface Area of a Cube The volume V and surface area S of a cube with edge of length s is given by the formulas 3
2
V = s and S = 6s .
s s
s
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Example: Volume of Surface Area of a Cube Find the volume and surface area of the cube below.
Solution 3
5 ft.
3
V = 5 =125 ft. 2
2
S = 6(5) = 150 ft.
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Volume of Surface Area of a Right Circular Cylinder The volume V and surface area S of a right circular cylinder with base radius r and height h is given by the formulas
V = π r h and S = 2π rh + 2π r . 2
2
h r
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Example: Volume of Surface Area of a Right Circular Cylinder Find the volume and surface area of the cylinder below. 10 m
Solution V = π (2) (10) = 40π ≈ 125.6 m 2
3
2m
S = 2π (2)(10) + 2π (2) = 48π ≈ 150.72 m 2
2 9-5-15
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Volume of Surface Area of a Sphere The volume V and surface area S of a sphere radius r is given by the formulas 4 3 V = π r and S = 4π r 2 . 3 r
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Example: Volume of Surface Area of a Sphere Find the volume and surface area of the sphere below. 9 in.
Solution 4 3 3 V = π (9) = 972π ≈ 3052.08 in. 3 S = 4π (9) 2 = 324π ≈ 1017.36 in.2 9-5-17 © 2008 Pearson Addison-Wesley. All rights reserved
Volume of Surface Area of a Right Circular Cone The volume V and surface area S of a right circular cone with base radius r and height h is given by the formulas 1 2 2 2 2 V = π r h and S = π r r + h + π r . 3 h r 9-5-18 © 2008 Pearson Addison-Wesley. All rights reserved
Example: Volume of Surface Area of a Right Circular Cone Find the volume and surface area of the cone below. 4m
3m
Solution 1 V = π (3) 2 (4) = 12π ≈ 37.68 m3 3
S = π (3) (3) + (4) + π (3) = 24π ≈ 75.36 m 2
2
2
2
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Volume of a Pyramid The volume V of a pyramid with height h and base of area B is given by the formulas 1 V = Bh. 3 h
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Example: Volume of a Pyramid Find the volume and surface area of the pyramid (rectangular base) below. 7 cm
Solution B = lw = 6(3) = 18 1 V = (18)(6) = 36 cm3 3
6 cm
3 cm
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