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A metal sphere of radius 6 in. is melted down
and recast as a solid cone with the same radius.
What is the lateral area of the cone?
12-5: Areas and Volumes of
Similar Solids
Formulas:
β€’ Prisms:
– 𝑽 = 𝑩𝒉
– 𝑻. 𝑨. = πŸπ‘© + 𝒑𝒉
β€’ Pyramids:
𝟏
πŸ‘
– 𝑽 = 𝑩𝒉
– 𝑻. 𝑨. = 𝑩 +
𝟏
𝒑𝒍
𝟐
β€’ Cylinders:
β€’ 𝑽 = π…π’“πŸ 𝒉
β€’ 𝑻. 𝑨. = πŸπ…π’“πŸ + πŸπ…π’“π’‰
β€’ Cones:
𝟏
β€’ 𝑽 = π…π’“πŸ 𝒉
πŸ‘
β€’ 𝑻. 𝑨. = π…π’“πŸ + 𝝅𝒓𝒍
β€’ Spheres:
‒𝑽=
‒𝑨=
πŸ’
π…π’“πŸ‘
πŸ‘
πŸ’π…π’“πŸ
Comparing Similar Solids
If the scale factor of two similar solids is 𝒂: 𝒃
1. The ratio of the corresponding perimeters (or any
lengths) is 𝒂: 𝒃
2. The ratio of the base areas, lateral areas, and total
areas
is π’‚πŸ : π’ƒπŸ
3. The ratio of the
volumes is π’‚πŸ‘ : π’ƒπŸ‘
True or false
1. All spheres are similar.
2. All right cylinders are similar.
3. All cubes are similar.
4. Two cones have base radii 9 m and 12 m, and heights
12 m and 18 m respectively. The cones are similar.
Two similar cylinders have circumferences of
18πœ‹ π‘π‘š and 24πœ‹ π‘π‘š. What is the ratio of their
volumes?
Two similar square pyramids have base areas 4 π‘š2
and 36 π‘š2 .
1. Find the ratio of the heights of the pyramids
2. If the height of the larger pyramid is 27 π‘š, what is
the height of the smaller pyramid?
Two similar cones have volumes of 16 𝑖𝑛3 and
54 𝑖𝑛3 . If the lateral (slant) height of the smaller
cone is 8 𝑖𝑛, what is the lateral (slant) height of
the large one?
p. 511: #1-17 odd, 12, 18
Chapter 12
on Friday!!!