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Circumference & Pi 3.14
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Find the perimeter of the trapezoid. Find the area of the trapezoid
9 6 17.5 5 Find the perimeter of the trapezoid. Find the area of the trapezoid A circle has a diameter of 30 feet. What is the radius? The radius of a circle is 7 inches. What is the diameter? 30 feet 7 in
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Circumference: The distance around the outside of a circle or think the perimeter of a circle Pi (π): The ratio of the circumference to diameter.
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Circumference of a Circle
C = πd = 2πr π(d) = π(2r) = 2πr
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π 3.14
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Videos SAV Lesson 4 ~ Circumference:
Simple (pi = 3) : Geeky: Nerd exact pi:
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Example 1a Find the circumference of the circle. Use 3.14 for π.
Write the circumference formula that uses diameter. C = πd Substitute the known values. C ≈ (3.14)(8) Multiply C ≈ 25.12 The circumference of ⊙H is about mm.
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Example 1b Find the circumference of the circle. Use 3.14 for π.
Write the circumference formula using the radius. C = 2πr Substitute the known values. C ≈ 2(3.14)(2.5) Multiply. C ≈ 15.7 The circumference of ⊙J is about 15.7 feet.
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Example 2 Natalya walked with her friend around a circular track.
The circumference of the track was meters. Find the approximate length of the track’s radius. Use 3.14 for π. Write the circumference formula C = 2πr Substitute the known values ≈ 2(3.14)r Multiply ≈ 6.28r Divide by 6.28 on each side. 30 ≈ r The radius of the track was approximately 30 m.
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Use 3.14 for in each problem.
Find the circumference of a circle with a diameter of 5 inches. Find the circumference of a circle with a radius of 5 inches. The circumference of a circle is mm. What is the diameter?
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Communication Prompt Why do you think the word “circumference” is used instead of “perimeter” for the distance around a circle? What is pi ()?
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