Circumference

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Circumference Areaof 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

• 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 C
3.14(8) C 25.12 The
circumference is 25.12 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 8. 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 50. 2 in

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Area of Circles

• The area of a circle is the product of and
  the square of the circles radius r.
• A r²
• radius

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Area of Circles

• Example Find the area of the circle

• A r²
• A 3.14(3)²
• A 3.14(9)
• A 28.26 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 50.24 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 ?
• Area of a Triangle bh
• Area of a Circle r²