1. There are 480 sophomores and 520 juniors in a high school
There are 480 sophomores and 520 juniors in a high school. Find the ratio of juniors to sophomores.
A. 10:8
B. 13:12
C. 19:17
D. 22:20
5-Minute Check 1

2. A strip of wood molding that is 33 inches long is cut into two pieces whose lengths are in the ratio of 7:4. What are the lengths of the two pieces?
A. 7 in., 4 in.
B. 14 in., 8 in.
C. 18 in., 15 in.
D. 21 in., 12 in.
5-Minute Check 2

3. A. 7
B. 8
C. 9
D. 10
5-Minute Check 3

4. A. 2.75
B. 3.25
C. 3.75
D. 4.25
5-Minute Check 4

5. A. 4
B. 3
C. 2
D. 1
5-Minute Check 5

6. The standard ratio of a photo’s width to its length is
The standard ratio of a photo’s width to its length is What is the length of a photo that has a width of 14 inches?
A. 9.3 inches
B. 17 inches
C. 20 inches
D. 56 inches
5-Minute Check 6

7. You used proportions to solve problems.
Use proportions to identify similar polygons.
Solve problems using the properties of similar polygons.
Then/Now

8. Concept

9. Use a Similarity Statement
If ΔABC ~ ΔRST, list all pairs of congruent angles and write a proportion that relates the corresponding sides.
Example 1

10. Use the similarity statement.
Use a Similarity Statement
Use the similarity statement.
ΔABC ~ ΔRST
Answer:
Congruent Angles: A  R, B  S, C  T
Example 1

11. If ΔGHK ~ ΔPQR, determine which of the following similarity statements is not true.
A. HGK  QPR B.
C. K  R
D. GHK  QPR
Example 1

12. Original Menu: New Menu:
Identify Similar Polygons
A. MENUS Tan is designing a new menu for the restaurant where he works. Determine whether the size for the new menu is similar to the original menu. If so, write the similarity statement and scale factor. Explain your reasoning.
Original Menu: New Menu:
Example 2

13. Step 1 Compare corresponding angles.
Identify Similar Polygons
Step 1 Compare corresponding angles.
Since all angles of a rectangle are right angles and right angles are congruent, corresponding angles are congruent.
Step 2 Compare corresponding sides.
Answer: Since corresponding sides are not proportional, ABCD is not similar to FGHK. So, the menus are not similar.
Example 2

14. Original Menu: New Menu:
Identify Similar Polygons
B. MENUS Tan is designing a new menu for the restaurant where he works. Determine whether the size for the new menu is similar to the original menu. If so, write the similarity statement and scale factor. Explain your reasoning.
Original Menu: New Menu:
Example 2

15. Step 1 Compare corresponding angles.
Identify Similar Polygons
Step 1 Compare corresponding angles.
Since all angles of a rectangle are right angles and right angles are congruent, corresponding angles are congruent.
Step 2 Compare corresponding sides.
Example 2

16. Identify Similar Polygons
Answer: Since corresponding sides are proportional, ABCD ~ RSTU. So, the menus are similar with a scale factor of __ 4 5
Example 2

17. A. BCDE ~ FGHI, scale factor = B. BCDE ~ FGHI, scale factor =
Original: New:
A. Lizzy is a wedding planner who is making invitations. Determine whether the size for the new invitations is similar to the original invitations used. If so, choose the correct similarity statement and scale factor.
A. BCDE ~ FGHI, scale factor =
B. BCDE ~ FGHI, scale factor =
C. BCDE ~ FGHI, scale factor =
D. BCDE is not similar to FGHI. __ 1 2 4 5 3 8
Example 2

18. A. BCDE ~ WXYZ, scale factor = B. BCDE ~ WXYZ, scale factor =
Original: New:
B. Lizzy is a wedding planner who is making invitations. Determine whether the size for the new invitations is similar to the original invitations used. If so, choose the correct similarity statement and scale factor.
A. BCDE ~ WXYZ, scale factor =
B. BCDE ~ WXYZ, scale factor =
C. BCDE ~ WXYZ, scale factor =
D. BCDE is not similar to WXYZ. __ 1 2 4 5 3 8
Example 2

19. A. The two polygons are similar. Find x.
Use Similar Figures to Find Missing Measures
A. The two polygons are similar. Find x.
Use the congruent angles to write the corresponding vertices in order.
polygon ABCDE ~ polygon RSTUV
Example 3

20. Write a proportion to find x.
Use Similar Figures to Find Missing Measures
Write a proportion to find x.
Similarity proportion
Cross Products Property
Multiply.
Divide each side by 4. Simplify.
Answer: x = __ 9 2
Example 3

21. B. The two polygons are similar. Find y.
Use Similar Figures to Find Missing Measures
B. The two polygons are similar. Find y.
Use the congruent angles to write the corresponding vertices in order.
polygon ABCDE ~ polygon RSTUV
Example 3

22. Similarity proportion
Use Similar Figures to Find Missing Measures
Similarity proportion
AB = 6, RS = 4, DE = 8, UV = y + 1
Cross Products Property
Multiply.
Subtract 6 from each side.
Divide each side by 6 and simplify.
Answer: y = __ 3 13
Example 3

23. A. The two polygons are similar. Solve for a.
A. a = 1.4
B. a = 3.75
C. a = 2.4
D. a = 2
Example 3

24. B. The two polygons are similar. Solve for b.
C. 7.2
D. 9.3
Example 3

25. Concept

26. Use a Scale Factor to Find Perimeter
If ABCDE ~ RSTUV, find the scale factor of ABCDE to RSTUV and the perimeter of each polygon.
Example 4

27. The scale factor ABCDE to RSTUV is or . AE VU 4 7
Use a Scale Factor to Find Perimeter
The scale factor ABCDE to RSTUV is or
___ AE VU __ 4 7
Write a proportion to find the length of DC.
Write a proportion.
4(10.5) = 7 ● DC Cross Products Property
6 = DC Divide each side by 7.
Since DC  AB and AE  DE, the perimeter of ABCDE is or 26.
Example 4

28. 4x = (26)(7) Cross Products Property x = 45.5 Solve.
Use a Scale Factor to Find Perimeter
Use the perimeter of ABCDE and scale factor to write a proportion. Let x represent the perimeter of RSTUV.
Theorem 7.1
Substitution
4x = (26)(7) Cross Products Property
x = 45.5 Solve.
Example 4

29. Use a Scale Factor to Find Perimeter
Answer: The perimeter of ABCDE is 26 and the perimeter of RSTUV is 45.5.
Example 4

30. If LMNOP ~ VWXYZ, find the perimeter of each polygon.
A. LMNOP = 40, VWXYZ = 30
B. LMNOP = 32, VWXYZ = 24
C. LMNOP = 45, VWXYZ = 40
D. LMNOP = 60, VWXYZ = 45
Example 4