Transcript Document

Circles
Formulas
Circumference = π * diameter
C = πd
Area = π * r2
A = πr2
When working with circles make sure you have
the diameter and radius.
Find the circumference and area of the circle below
8cm
Radius = 8
Diameter = 16
C = πd
C = π*16
A = πr2
A = π*82
C = 50.24cm
A = 64π = 200.96cm2
A circle has a diameter of 12π units. What is it’s area?
(express in π units)
Diameter = 12π
Radius =
6π
A = πr2
A = π*(6π)2
A = 36π2*π = 36π3units2
What is the area of the shaded region?
20cm
Diameter = 20cm
Radius =
10cm
A(square) = 20 * 20 = 400cm2
A(circle) = πr2 = π*(10)2 = 100π = 314cm2
A (shaded) = 400 - 314 = 86cm2
What is the area of a circle that has a circumference
of 94.2cm
C = πd
A = πr2
94.2 = πd
A = π(15)2
94.2 = d
π
A = 225π
d = 30cm
r = 15cm
A = 706.5cm2
What is the circumference of a circle that has an
area of 452.16cm2
A = πr2
C = πd
452.16 = πr2
C = π*24
452.16 = r2
π
C = 75.36cm
r2 = 144cm
r = 12cm
d = 24cm