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# Perimeter

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### Perimeter

1. 1. Perimeter Perimeter of a Rectangle, Polygons and using Algebra!
2. 2. What is Perimeter? Suppose you need to put a ribbon border around a picture . How would you decide how long the ribbon needs to be? One way would be to measure each side and add them together! The sum of all the sides together is called the Perimeter.
3. 3. Perimeter of a Rectangle To find the perimeter of a rectangle, add all the sides. Perimeter = length + length + width + width *Remember* in a rectangle, opposite sides are equal. That means we can rewrite the formula as: P= 2l + 2w Length Length WidthWidth
4. 4. Practice What is the Perimeter of the following rectangle? P= 2l + 2w P=2(10)+2(5) = 20 +10 = 30 cm 5 cm 10 cm 10 cm 5 cm
5. 5. Practice Perimeter Click on the right answer! 1. A. 30 B. 46 C. 23 D. 165 A. 150 C. 236 B. 86 D. 193 15 88 15 75 43 2.
6. 6. Perimeter of a Polygon How could we find perimeter for other shapes? If all sides are given, we can add them up! P= 8 + 8 +3 + 3 +11 P= 33 8 11 8 3 3
7. 7. Practice Find the perimeter of the polygon below: 5 1 7 5 7 10 5 2 5 A. 47 B. 50 C. 44 D. 60
8. 8. Practice: Find the perimeter of the polygon below: 22 13 12 9 8 6 A. 47 B. 50 C. 60 D. 70 A. 47
9. 9. Perimeter and Algebra Using what we learned about perimeter, we could be able to solve for a missing side: Given that the Perimeter of the polygon is 35, find the value of x. 35=5 + 7 + 4 + 9 + x 35=25 + x 10=x x 7 9 4 5
10. 10. Perimeter and Algebra Perimeter could also be written in terms of a variable. Let’s see how: If we add all the sides we get: P = 3x + 3x + x + 1 + x + 1 P = 8x + 2 If we were told the sum of all sides is 26, how could we find each side? We know 8x + 2 = Perimeter (sum of all sides) So, 8x +2 = 26 If we solve for x we should get, x = 3 Thus, the length of 3x = 3(3) =9 and the width of x+1 = 3 +1 =4 3x 3x X+1 X+1
11. 11. Practice Given that the Perimeter of the rectangle is 86, find the measure of each side. 2x+3 2x+3 2x 2x A. 10 and 20 B. 20 and 23 C. 10 and 13 D. 20 and 13
12. 12. Practice Given the sum of the sides of the regular hexagon is 125 , find the value of x X + 5 A. 10 B. 120 C. 50 D. 20
13. 13. Resources