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Lesson Menu Five-Minute Check (over Lesson 7–1) Then/Now New Vocabulary Key Concept: Similar Polygons Example 1:Use a Similarity Statement Example 2:Real-World Example: Identify Similar Polygons Example 3:Use Similar Figures to Find Missing Measures Theorem 7.1: Perimeter of Similar Polygons Example 4:Use a Scale Factor to Find Perimeter

Over Lesson 7–1 A.A B.B C.C D.D 5-Minute Check 1 A.10:8 B.13:12 C.19:17 D.22:20 There are 480 sophomores and 520 juniors in a high school. Find the ratio of juniors to sophomores.

Over Lesson 7–1 A.A B.B C.C D.D 5-Minute Check 2 A.7 in., 4 in. B.14 in., 8 in. C.18 in., 15 in. D.21 in., 12 in. 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?

Over Lesson 7–1 A.A B.B C.C D.D 5-Minute Check 3 A.7 B.8 C.9 D.10

Over Lesson 7–1 A.A B.B C.C D.D 5-Minute Check 4 A.2.75 B.3.25 C.3.75 D.4.25

Over Lesson 7–1 A.A B.B C.C D.D 5-Minute Check 5 A.4 B.3 C.2 D.1

Over Lesson 7–1 A.A B.B C.C D.D 5-Minute Check 6 A.9.3 inches B.17 inches C.20 inches D.21 inches 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?

Then/Now You used proportions to solve problems. (Lesson 7–1) Use proportions to identify similar polygons. Solve problems using the properties of similar polygons.

Vocabulary similar polygons similarity ratio scale factor

Concept

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

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

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

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

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

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

A.A B.B C.C D.D Example 2 A. Thalia 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. __ Original:New:

A.A B.B C.C D.D Example 2 B. Thalia 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. __ Original:New:

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

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

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

A.A B.B C.C D.D Example 3 A.1.2 B.2.1 C.7.2 D.9.3 B. The two polygons are similar. Solve for b.

Concept

Example 4 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 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. Since DC  AB and AE  DE, the perimeter of ABCDE is or 26. Write a proportion. 4(10.5)= 7 ● DCCross Products Property 6= DCDivide each side by 7.

Example 4 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= 45.5Solve.

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

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

End of the Lesson