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Perimeter and Area of Similar Figures

7 th Grade Math Lesson Objective: Students will find the perimeter and area of similar figures. Perimeter and Area of Similar Figures. Concept – Perimeter. How to find Add each side length of an object Similar Figures Rule P (New) = P (Original) • SF Scale Factor New / Original.

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Perimeter and Area of Similar Figures

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  1. 7th Grade Math Lesson Objective: Students will find the perimeter and area of similar figures. Perimeter and Area of Similar Figures

  2. Concept – Perimeter • How to find • Add each side length of an object • Similar Figures Rule • P(New)= P(Original)• SF • Scale Factor • New/Original

  3. Example 1 • Two rectangles are similar. One has a length of 6 inches and a perimeter of 24 inches. The other has a length of 7 inches. What is the perimeter of this rectangle? SF = 7/6 P = 24 • 7/6 P = 28 in

  4. Example 2 L P 18 m 24 m Q R M N P = 64 m LMN is similar to PQR P = 64 • 3/4 SF = 18/24 or 3/4 P = 48 m

  5. Concept – Area • How to find • Rectangle = bh • Triangle = ½bh • Similar Figures Rule • A(New)= A(Original)• SF2 • Scale Factor • New/Original

  6. Example 3 • The Eddingtons have a 5-foot by 8-foot porch on the front of their house. They are building a similar porch on the back with double the dimensions. Find the area of the back porch. A = 40 • 22 SF = 2 A = 40 • 4 A = 160 ft2

  7. Example 4 • Malia is painting a mural on her bedroom wall. The image she is reproducing is 1/20 of her wall and has an area of 36 square inches. Find the area of the mural. A = 36 • 202 SF = 20 A = 36 • 400 A = 14,400 in2

  8. Example 5 • A company wants to reproduce the size of its logo by one fourth to use on business cards. If the area of the original logo is 4 square inches, what is the area of the logo that will be used on the business cards? A = 4 • (¼)2 SF = ¼ A = 4 • 1/16 A = 0.25 in2

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