# 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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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?

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

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

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.

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

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

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.

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)

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 ? ? ??

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

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

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

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