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**Circumference & Area of a Circle**

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**Definitions Circumference: The distance around a circle.**

Diameter (d): a line that passes through the center of a circle that has its endpoints on the circle. Radius (r): half the diameter d = 20, then r = 10 r = 15, then d = 30

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**Circumference C = d Diameter**

To find the circumference multiply times the diameter, where equals 3.14 C = d Diameter

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**Circumference Example: Find the circumference Circumference = d**

The circumference is in Diameter = 8 in

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**Circumference Example: Find the circumference radius = 10 cm**

Circumference = d Diameter = 2r = 2 (10) = 20 C = 3.14(20) C = 62.8 The circumference is 62.8 cm

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**Your Turn…. Find the circumference**

pg. 426 # 7-9 No naked numbers. 7. C = d C = d C = 3.14(12) C = 3.14(3) C = 37.7m C = 9.4 ft 9. C = d C = 3.14 (16) C = in

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Area of Circles The area of a circle is the product of and the square of the circle’s radius r. A = r² radius

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**Area of Circles A = r² A = 3.14(3)² A = 3.14(9) A = 28.26 m²**

Example: Find the area of the circle A = r² A = 3.14(3)² A = 3.14(9) A = m² The area of the circle is 28.26m² r = 3 m

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**Area of Circles A = r² Radius = 4 in A = 3.14(4)² A = 3.14(16)**

A = in² The area of the circle is 50.24in² d = 8 in

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**Lets Review Perimeter = Sum of all sides Circumference = d**

Area of a Rectangle = ω Area of a Triangle = bh Area of a Circle = r²

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