Circumference & Area
Parts of a CircleParts of a Circle
diameter
radius
d = 2r
and
r = d2
1
Circumference(Distance around a circle)
C = d or C = 2 r
8 in.
C = 3.14(8)C = 25.12 in.
= 3.14
C = 2(3.14)(4)C = 25.12 in
4 in.
Give it a try!1. If the diameter is 10 feet, what is the
radius?
2. If the radius is 3.2 inches, what is the diameter?
3. Find the circumference:
4. Find the circumference:
15 cm
3 mm
Give it a try!1. If the diameter is 10 feet, what is the
radius? r = 5 feet2. If the radius is 3.2 inches, what is the
diameter? d = 6.4 in.3. Find the circumference:C = 3.14 x 15 = 47.1 cm
4.Find the circumference:C = 2 x 3.14 x 3 = 18.84 mm
15 cm
3 mm
Area of a Circle(The inside of the circle)
A = r A = r
2
3 m
A = 3.14(3 )A = 28.26 m
2
10 ind = 10 inr = 5 in
A = 3.14(5 )A = 78.5 in2
2 22
You try!
A = 2r
7 in 20 ft.
You try!
2
2
2
A = 2
rA = 3.14(7 )A = 153.86 in2
20 ft.
d = 20, so r = 10A = rA = 3.14(10 )A = 314 ft
2
7 in
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