1. Circumference & Area of a Circle

2. 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

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

4. Circumference Example: Find the circumference Circumference = d
The circumference is in
Diameter = 8 in

5. 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

6. 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

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

8. 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

9. 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

10. Lets Review Perimeter = Sum of all sides Circumference = d
Area of a Rectangle = ω
Area of a Triangle = bh
Area of a Circle = r²