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Similar Polygons

Similar Polygons. Chapter 7-2. Identify similar figures. Solve problems involving scale factors. similar polygons. scale factor. Standard 11.0 Students determine how changes in dimensions affect the perimeter , area, and volume of common geometric figures and solids. Lesson 2 MI/Vocab.

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Similar Polygons

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  1. Similar Polygons Chapter 7-2

  2. Identify similar figures. • Solve problems involving scale factors. • similar polygons • scale factor Standard 11.0 Students determine how changes in dimensions affect the perimeter, area, and volume of common geometric figuresand solids. Lesson 2 MI/Vocab

  3. E A F H G D B C Similar Polygons ABCD ~ EFGH A  E B  F C  G D  H • Have congruent corresponding angles. • Have proportional corresponding sides. • “~” means “is similar to”

  4. 6 B A 9 15 C 12 D 4 Y W 6 10 Z 8 X Writing Similarity Statements A  W B  Y C  Z D  X • Decide if the polygons are similar. If they are, write a similarity statement. All corr. sides are proportionate and all corr. angles are  ABCD ~ WYZX

  5. Scale Factor • The ratio of the lengths of two corresponding sides. • In the previous example the scale factor is 3:2.

  6. Similar Polygons A.Determine whether each pair of figures is similar. Justify your answer. The vertex angles are marked as 40º and 50º, so they are not congruent. Lesson 2 Ex1

  7. Since both triangles are isosceles, the base angles in each triangle are congruent. In the first triangle, the base angles measure and in the second triangle, the base angles measure Similar Polygons Answer: None of the corresponding angles are congruent, so the triangles are not similar. Lesson 2 Ex1

  8. Similar Polygons B.Determine whether each pair of figures is similar. Justify your answer. All the corresponding angles are congruent. Lesson 2 Ex1

  9. Similar Polygons Now determine whether corresponding sides are proportional. The ratios of the measures of the corresponding sides are equal. Answer: The ratio of the measures of the corresponding sides are equal and the corresponding angles are congruent, so ΔABC ~ ΔRST. Lesson 2 Ex1

  10. A.Determine whether the pair of figures is similar. A. Yes, ΔAXE ~ ΔWRT. B. Yes, ΔAXE ~ ΔRWT. C. No, the Δ's are not ~. D. not enough information Lesson 2 CYP1

  11. B.Determine whether the pair of figures is similar. A. Yes, ΔTRS ~ ΔNGA. B. Yes, ΔTRS ~ ΔGNA. C. No, the Δ's are not ~. D. not enough information Lesson 2 CYP1

  12. ARCHITECTURE An architect prepared a 12-inch model of a skyscraper to look like a real 1100-foot building. What is the scale factor of the model compared to the real building? Before finding the scale factor you must make sure that both measurements use the same unit of measure. 1 foot = 12 inches Lesson 2 Ex2

  13. Answer: The ratio comparing the two heights is or 1:1100. The scale factor is , which means that the model is the height of the real skyscraper. Animation:Similar Polygons Lesson 2 Ex2

  14. A. B. C. D. A space shuttle is about 122 feet in length. The Science Club plans to make a model of the space shuttle with a length of 24 inches. What is the scale factor of the model compared to the real space shuttle? Lesson 2 CYP2

  15. Proportional Parts and Scale Factor A.The two polygons are similar. Write a similarity statement. Then find x,y, and UV. Use the congruent angles to write the corresponding vertices in order. polygon ABCDE ~ polygon RSTUV Lesson 2 Ex3

  16. Proportional Parts and Scale Factor Now write proportions to find x and y. To find x: Similarity proportion Cross products Multiply. Divide each side by 4. Lesson 2 Ex3

  17. Proportional Parts and Scale Factor To find y: Similarity proportion AB = 6, RS = 4, DE = 8, UV = y + 1 Cross products Multiply. Subtract 6 from each side. Divide each side by 6 and simplify. Lesson 2 Ex3

  18. Proportional Parts and Scale Factor Lesson 2 Ex3

  19. Proportional Parts and Scale Factor B. The two polygons are similar. Find the scale factor of polygon ABCDE to polygon RSTUV. The scale factor is the ratio of the lengths of any two corresponding sides. Answer: Lesson 2 Ex3

  20. A. The two polygons are similar. Write a similarity statement. A.TRAP ~ OZDL B.TRAP ~ OLDZ C.TRAP ~ ZDLO D.TRAP ~ ZOLD Lesson 2 CYP3

  21. B. The two polygons are similar. Solve for a. A.a = 1.4 B.a = 3.75 C.a = 2.4 D.a = 2 Lesson 2 CYP3

  22. A.b = 7.2 B.b = 1.2 C. D.b = 7.2 C. The two polygons are similar. Solve for b. Lesson 2 CYP3

  23. A.7.2 B.1.2 C.2.4 D. D. The two polygons are similar. Solve for ZO. Lesson 2 CYP3

  24. A. B. C. D. E. The two polygons are similar. What is the scale factor of polygon TRAP to polygon ZOLD? • A • B • C • D Lesson 2 CYP3

  25. Write proportions for finding side measures. Let one long side of each WXYZ and PQRS be and one short side of each WXYZ and PQRS be Enlargement or Reduction of a Figure Rectangle WXYZ is similar to rectangle PQRS with a scale factor of 1.5. If the length and width of PQRS are 10 meters and 4 meters, respectively, what are the length and width of rectangle WXYZ? Lesson 2 Ex4

  26. WXYZPQRS WXYZPQRS Enlargement or Reduction of a Figure Lesson 2 Ex4

  27. Quadrilateral GCDE is similar to quadrilateral JKLMwith a scale factor of . If two of the sides of GCDEmeasure 7 inches and 14 inches, what are the lengthsof the corresponding sides of JKLM? A. 9.8 in, 19.6 in B. 7 in, 14 in C. 6 in, 12 in D. 5 in, 10 in Lesson 2 CYP4

  28. The scale on the map of a city is inch equals 2 miles. On the map, the width of the city at its widest point is inches. The city hosts a bicycle race across town at its widest point. Tashawna bikes at 10 miles per hour. How long will it take her to complete the race? Explore Every equals 2 miles. The distance across the city at its widest point is Scales on Maps Lesson 2 Ex5

  29. Plan Create a proportion relating the measurements to the scale to find the distance in miles. Then use the formula to find the time. Divide each side by 0.25. Scales on Maps Solve Cross products The distance across the city is 30 miles. Lesson 2 Ex5

  30. Scales on Maps Divide each side by 10. It would take Tashawna 3 hours to bike across town. Examine To determine whether the answer is reasonable, reexamine the scale. If 0.25 inches = 2 miles, then 4 inches = 32 miles. The distance across the city is approximately 32 miles. At 10 miles per hour, the ride would take about 3 hours. The answer is reasonable. Answer: 3 hours Lesson 2 Ex5

  31. An historic train ride is planned between two landmarks on the Lewis and Clark Trail. The scale on a map that includes the two landmarks is 3 centimeters = 125 miles. The distance between the two landmarks on the map is 1.5 centimeters. If the train travels at an average rate of 50 miles per hour, how long will the trip between the landmarks take? A. 3.75 hr B. 1.25 hr C. 5 hr D. 2.5 hr Lesson 2 CYP5

  32. Homework Chapter 7-2 • Pg 392 1 – 6, 8 – 11, 14 – 19, {28 – 36, (9th and 10th grade)}, 37 – 41, 60 – 64 evens, 71 – 76

  33. Forced Perspective

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