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Lessons 6.5 Circumference and 8.5 Area of a Circle PI π = Ratio of Circumference to Diameter HOMEWORK: Lesson 6.5/1-13 Lesson 8.5/1-10

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Circumference

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Finding the Circumference You can find the circumference of a circle by using the formula- Circumference = π x diameter For Example- Circumference= π * 10 C = 10π cm C ≈ 10*3.14 C ≈ 31,4 cm 10cm exact approx.

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Example 1: Solution: The diameter of a circle is 3 centimeters. What is the circumference? C = π d C = 3 π cm C ≈ 9.42 cm C ≈ 3 (3.14) cm exact approx.

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Example 2: The radius of a circle is 2 inches. What is the circumference? Solution: C = 4 π in C ≈ 4 * 3.14 C ≈ in exact approx. C = 2 π 2 C = 2 π r

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Example 3: The circumference of a circle is 15.7 centimeters. What is the diameter? Solution: 15.7 cm = πd d≈ 5 cm exact approx.

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Example 4: The distance around a carousel is yards. What is the radius? C = 2 π r = 2 π r r≈ 3.5 yds exact approx.

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Finding the Area Area= π * radius 2 7cm

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Find the area of a circle given the diameter

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Circumference Area If C = 25π cm Find Area exact approx.

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Circumference Area exact approx.

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Circumference Area exact approx.

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Sketch and Solve 12 in exact approx. exact approx.

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The area of a circle Use π = 3.14 to find the area of the following circles: A = πr 2 2 cm = 3.14 × 2 2 = cm 2 A = πr 2 10 m = 3.14 × 5 2 = 78.5 m 2 A = πr 2 23 mm = 3.14 × 23 2 = mm 2 A = πr 2 78 cm = 3.14 × 39 2 = cm 2

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Finding the Area A= π x r 2 exact approx.

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