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8-1C The Circumference of a Circle What is circumference? What is pi? What is the symbol for pi? What are the formulas for the circumference of a circle?

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Circumference Circumference is the distance around a circle. Perimeter is to a rectangle as circumference is to a circle.

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Measure up Measure the circumference and diameter of three circular objects. Calculate the ratio of the circumference to the diameter to the nearest tenth. objectcircumferencediameterratio Mug Tube Cylinder

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Circumference to diameter ratio The ratio of the circumference to the diameter of a circle is the number pi (π). Pi is an irrational number. Its’ decimal representation does not terminate or follow a repeating pattern. We use 3.14 as the value for π. Find the π button on your calculator.

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Definition The number π is the ratio of the circumference of any circle to its diameter.

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Theorems The circumference of a circle is the product of π and its diameter d. C = πd The circumference of a circle is twice the product of π and its radius r C = 2πr

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Exact or Approximate? Answers from problems with π in them can be written two ways. Exact answers leave the π symbol as part of the answer. Approximate answers use the decimal approximation (3.14…) and the answer is in decimal form.

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If the radius of סּC is 4 cm, what is the circumference to the nearest tenth? C = 2πr C = πd Which formula should you use? Which formula has the variables you are given in the problem? C = 2π(4) = 8π (exact answer) ≈ 25.1 cm (approximate answer)

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What is the circumference of the pan? Round your answer to the nearest tenth. C = π(8) = 8π (exact) ≈ 25.1 in (approximate) 8 in C = πdC = 2πr ? ? ??

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The circumference of a trash can lid is 22π. What is its diameter? What formula do you use? C = πd The 22π replaces what letter? C What variable do you solve for? d 22π = πd (divide both sides by π) d = 22

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What is circumference? Circumference is the distance around a circle. What is pi? The ratio of the circumference to the diameter of a circle. What is the symbol for pi? π What are the formulas for the circumference of a circle? C = 2πrC = πd

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Assignment 8-1C Page 553, 1-8, 20-26 No formulas with numbers No credit

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