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Holt Geometry 10-4 Surface Area of Prisms and Cylinders 10-4 Surface Area of Prisms and Cylinders Holt Geometry

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10-4 Surface Area of Prisms and Cylinders Warm Up Find the perimeter and area of each polygon. 1. a rectangle with base 14 cm and height 9 cm 2. a right triangle with 9 cm and 12 cm legs 3. an equilateral triangle with side length 6 cm

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Learn and apply the formula for the surface area of a prism. Learn and apply the formula for the surface area of a cylinder. Objectives

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders lateral face lateral edge right prism oblique prism altitude surface area lateral surface axis of a cylinder right cylinder oblique cylinder Vocabulary

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Prisms and cylinders have 2 congruent parallel bases. A lateral face is not a base. The edges of the base are called base edges. A lateral edge is not an edge of a base. The lateral faces of a right prism are all rectangles. An oblique prism has at least one nonrectangular lateral face.

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders An altitude of a prism or cylinder is a perpendicular segment joining the planes of the bases. The height of a three-dimensional figure is the length of an altitude. Surface area is the total area of all faces and curved surfaces of a three-dimensional figure. The lateral area of a prism is the sum of the areas of the lateral faces.

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders The net of a right prism can be drawn so that the lateral faces form a rectangle with the same height as the prism. The base of the rectangle is equal to the perimeter of the base of the prism.

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders The surface area of a right rectangular prism with length ℓ, width w, and height h can be written as S = 2ℓw + 2wh + 2ℓh.

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders The surface area formula is only true for right prisms. To find the surface area of an oblique prism, add the areas of the faces. Caution!

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Example 1A: Finding Lateral Areas and Surface Areas of Prisms Find the lateral area and surface area of the right rectangular prism. Round to the nearest tenth, if necessary.

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Example 1B: Finding Lateral Areas and Surface Areas of Prisms Find the lateral area and surface area of a right regular triangular prism with height 20 cm and base edges of length 10 cm. Round to the nearest tenth, if necessary.

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders The lateral surface of a cylinder is the curved surface that connects the two bases. The axis of a cylinder is the segment with endpoints at the centers of the bases. The axis of a right cylinder is perpendicular to its bases. The axis of an oblique cylinder is not perpendicular to its bases. The altitude of a right cylinder is the same length as the axis.

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Example 2A: Finding Lateral Areas and Surface Areas of Right Cylinders Find the lateral area and surface area of the right cylinder. Give your answers in terms of . L = 2rh = 2(8)(10) = 160 in 2 The radius is half the diameter, or 8 in. S = L + 2r 2 = 160 + 2(8) 2 = 288 in 2

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Example 2B: Finding Lateral Areas and Surface Areas of Right Cylinders Find the lateral area and surface area of a right cylinder with circumference 24 cm and a height equal to half the radius. Give your answers in terms of . Step 1 Use the circumference to find the radius. C = 2r Circumference of a circle 24 = 2r Substitute 24 for C. r = 12 Divide both sides by 2.

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Example 2B Continued Step 2 Use the radius to find the lateral area and surface area. The height is half the radius, or 6 cm. L = 2rh = 2(12)(6) = 144 cm 2 S = L + 2r 2 = 144 + 2(12) 2 = 432 in 2 Lateral area Surface area Find the lateral area and surface area of a right cylinder with circumference 24 cm and a height equal to half the radius. Give your answers in terms of .

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Find the lateral area and surface area of a cylinder with a base area of 49 and a height that is 2 times the radius. Check It Out! Example 2 Continued

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Example 3: Finding Surface Areas of Composite Three-Dimensional Figures Find the surface area of the composite figure.

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Example 3 Continued Two copies of the rectangular prism base are removed. The area of the base is B = 2(4) = 8 cm 2. The surface area of the rectangular prism is.. A right triangular prism is added to the rectangular prism. The surface area of the triangular prism is

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders The surface area of the composite figure is the sum of the areas of all surfaces on the exterior of the figure. Example 3 Continued S = (rectangular prism surface area) + (triangular prism surface area) – 2(rectangular prism base area) S = 52 + 36 – 2(8) = 72 cm 2

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Check It Out! Example 3 Find the surface area of the composite figure. Round to the nearest tenth.

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Check It Out! Example 3 Continued Find the surface area of the composite figure. Round to the nearest tenth. The surface area of the rectangular prism is S =Ph + 2B = 26(5) + 2(36) = 202 cm 2. The surface area of the cylinder is S =Ph + 2B = 2(2)(3) + 2(2) 2 = 20 ≈ 62.8 cm 2. The surface area of the composite figure is the sum of the areas of all surfaces on the exterior of the figure.

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders S = (rectangular surface area) + (cylinder surface area) – 2(cylinder base area) S = 202 + 62.8 — 2()(2 2 ) = 239.7 cm 2 Check It Out! Example 3 Continued Find the surface area of the composite figure. Round to the nearest tenth.

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Always round at the last step of the problem. Use the value of given by the key on your calculator. Remember!

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Example 4: Exploring Effects of Changing Dimensions The edge length of the cube is tripled. Describe the effect on the surface area.

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Example 4 Continued original dimensions:edge length tripled: Notice than 3456 = 9(384). If the length, width, and height are tripled, the surface area is multiplied by 3 2, or 9. S = 6ℓ 2 = 6(8) 2 = 384 cm 2 S = 6ℓ 2 = 6(24) 2 = 3456 cm 2 24 cm

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Check It Out! Example 4 The height and diameter of the cylinder are multiplied by. Describe the effect on the surface area.

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders original dimensions:height and diameter halved: S = 2(11 2 ) + 2(11)(14) = 550 cm 2 S = 2(5.5 2 ) + 2(5.5)(7) = 137.5 cm 2 11 cm 7 cm Check It Out! Example 4 Continued Notice than 550 = 4(137.5). If the dimensions are halved, the surface area is multiplied by

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Lesson Quiz: Part I Find the lateral area and the surface area of each figure. Round to the nearest tenth, if necessary. 1. a cube with edge length 10 cm 2. a regular hexagonal prism with height 15 in. and base edge length 8 in. 3. a right cylinder with base area 144 cm 2 and a height that is the radius

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Holt Geometry 10-4 Surface Area of Prisms and Cylinders Lesson Quiz: Part II 4. A cube has edge length 12 cm. If the edge length of the cube is doubled, what happens to the surface area? 5. Find the surface area of the composite figure.

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