1. Circles
Formulas
Circumference = π * diameter
C = πd
Area = π * r2
A = πr2
When working with circles make sure you have the diameter and radius.

2. Find the circumference and area of the circle below
8cm
Radius =
Diameter = 8 16
C = πd
A = πr2
C = π*16
A = π*82
C = 50.24cm
A = 64π = cm2

3. A circle has a diameter of 12π units. What is it’s area?
(express in π units)
Diameter =
Radius =
12π 6π
A = πr2
A = π*(6π)2
A = 36π2*π = 36π3units2

4. What is the area of the shaded region?
20cm
Diameter =
Radius =
20cm
10cm
A(square) =
20 * 20 = 400cm2
A(circle) =
πr2 = π*(10)2
= 100π = 314cm2
A (shaded)
= = 86cm2

5. 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
A = 706.5cm2
d = 30cm
r = 15cm

6. What is the circumference of a circle that has an area of 452.16cm2
C = πd
= πr2
C = π*24
= r2 π
C = 75.36cm
r2 = 144cm
r = 12cm
d = 24cm