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Published byHelen Ray Modified over 9 years ago
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How can you find the circumference of a circle if you only know the area? For Example A circle has an area 16 π cm 2. What is the circumference of the circle?
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In this lesson you will learn how to find the circumference of a circle by using the measure of area.
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Let’s Review Area of a Circle = π r 2 Circumference of a Circle= π d or 2 π r
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The reverse of squaring a number is finding the square root. 3 2 = 9
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A Common Mistake Finding the square root of a number is not the same as dividing it by 2. Wrong Correct
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Let’s Review Core Lesson Bill has a circular garden that he wants to put a fence around. He knows that the area of a garden is 16 π yds 2. How much fencing does Bill need to go around the circumference of the garden? A = 16 π yds 2 A = π r 2 C = 2 π r r 2 = 16 yds 2 r = 4 yds 4 yds C = 2 π (4 yds) C = 8 π yds
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Let’s Review Core Lesson A circle has an approximate area of 28.26 ft 2. If 3.14 was used for pi, what is the circumference of the circle? A = π r 2 28.26 ft 2 = 3.14r 2 3.14 3.14 9 ft 2 = r 2 3 ft = r C = 2 π r C = 2(3.14)3 C = 18.84 ft
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In this lesson you have learned how to find the circumference of a circle by using the measure of the area.
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Let’s Review Guided Practice A circle has an area of 25 π cm 2. What is the circumference of the circle?
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Let’s Review Extension Activities The area of a circle is 16 π meters 2. Stephanie concluded that the circumference of the circle would be 16 π. She stated “the radius would be 8 meters since the square root of 16 is 8.” What mistake did Stephanie make. Write an explanation describing how to fix her mistake.
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Let’s Review Extension Activities A circle inside of a square touches the square at each edge as shown below. If the circle has an area of 25 π feet 2, find the area of the square.
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Let’s Review Quick Quiz Find the circumference of the circle that has an area of 81 π m 2. A circle has an area of 113.04 cm 2. What is the circumference of the circle?
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