1. Identify congruent or similar solids.
Use properties of similar solids.
Splash Screen

2. similar solids
congruent solids
Vocabulary

3. Concept

4. Concept

5. Identify Similar and Congruent Solids
A. Determine whether the pair of solids is similar, congruent, or neither. If the solids are similar, state the scale factor.
Find the ratios between the corresponding parts of the square pyramids.
Substitution
Simplify.
Example 1

6. Substitution Simplify. Substitution Simplify.
Identify Similar and Congruent Solids
Substitution
Simplify.
Substitution
Simplify.
Answer: The ratios of the measures are equal, so we can conclude that the pyramids are similar. Since the scale factor is not 1, the solids are not congruent.
Example 1

7. Compare the ratios between the corresponding parts of the cones.
Identify Similar and Congruent Solids
B. Determine whether the pair of solids is similar, congruent, or neither. If the solids are similar, state the scale factor.
Compare the ratios between the corresponding parts of the cones.
Example 1

8. Substitution Simplify. Substitution
Identify Similar and Congruent Solids
Substitution
Simplify.
Substitution
Answer: Since the ratios are not the same, the cones are neither similar nor congruent.
Example 1

9. A. Determine whether the pair of solids is similar, congruent, or neither.
A. similar
B. congruent
C. neither
Example 1

10. B. Determine whether the pair of solids is similar, congruent, or neither.
A. similar
B. congruent
C. neither
Example 1

11. Concept

12. First, find the scale factor.
Use Similar Solids to Write Ratios
Two similar cones have radii of 9 inches and 12 inches. What is the ratio of the volume of the smaller cone to the volume of the larger cone?
First, find the scale factor.
Write a ratio comparing the radii.
Example 2

13. If the scale factor is , then the ratio of the volumes is .
Use Similar Solids to Write Ratios
If the scale factor is , then the ratio of the volumes is
Answer: So, the ratio of the volume is 27:64.
Example 2

14. Two similar cones have radii of 5 inches and 15 inches
Two similar cones have radii of 5 inches and 15 inches. What is the ratio of the volume of the smaller cone to the volume of the larger cone?
A. 1:3
B. 1:9
C. 1:27
D. 1:81
Example 2

15. Understand You know the volume of the softballs.
Use Similar Solids to Find Unknown Values
SOFTBALLS The softballs shown are similar spheres. Find the radius of the smaller softball if the radius of the larger one is about 1.9 cubic inches.
Understand You know the volume of the softballs.
Plan Use Theorem 12.1 to write a ratio comparing the volumes. Then find the scale factor and use it to find r.
Example 3

16. Write a ratio comparing volumes.
Use Similar Solids to Find Unknown Values
Solve
Write a ratio comparing volumes. =
Simplify. ≈
Write as
Example 3

17. Find the cross products.
Use Similar Solids to Find Unknown Values
Ratio of radii
Scale factor
Find the cross products.
r ≈ 1.45
Solve for r.
Answer: So, the radius of the smaller softball is about 1.45 inches.
Example 3

18. Use Similar Solids to Find Unknown Values
Check 
Example 3

19. CONTAINERS The containers below are similar cylinders
CONTAINERS The containers below are similar cylinders. Find the height h of the smaller container.
A. 2 in.
B. 3 in.
C. 4 in.
D. 5 in.
Example 3

20. Homework
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Concept