1. Find the area and circumference of each circle.
Leave answers in terms of π.
C = 2 • π • r , A = π • r2 1)
C = 2 • π • 4 m
= 8π m
4 m
A = π • (4 m)2
= 16π m2
C = 2 • π • 9 cm
= 18π cm
2) r = 9 cm
A = π • (9 cm)2
= 81π cm2
C = 2 • π • 6 in
= 12π in
3) d = 12 in
A = π • (6 in)2
= 36π in2

2. 18.06 Area & Perimeter of Irregular Figures

3. Recall: Area Formulas Recall: Perimeter
Rectangle:
A = b • h
Parallelogram:
A = b • h
Triangle:
A = ½ • b • h
Trapezoid:
A = ½ • h • (b1 + b2)
Circle:
A = π • r2
Recall: Perimeter
Perimeter is defined as the distance around the figure, adding up the lengths of the sides.
Rectangle:
P = 2b + 2h
Circle:
C = 2 • π • r

4. Some figures are a composition of two or more figures.
This type of figure is called a compound polygon.
Examples:
To find the area , divide the figure up into smaller pieces and use the formulas to find each area and combine them.

5. Find the perimeter and area.7
To find the perimeter, find the two missing sides. 2 2 10 8
P =
= 34 5
To find the area, find the area of the 2 rectangles.
The area of the top rectangle is 7 • 2
= 14
The area of the bottom rectangle is 5 • 8
= 40
The area of the figure is
= 54

6. Find the perimeter and area.
To find the perimeter, find the missing side. 15 9
P = 7 6 7
= 50 12
To find the area, find the area of the triangle and parallelogram.
The area of the triangle is ½ • 12 • 9
= 54
The area of the parallelogram is 12 • 6
= 72
The area of the figure is
= 126

7. Find the area of the shaded region.3 3
Find the area of the entire rectangle.
A = b • h = 12 • 6 = 72
Find the area of one circle, then double it.
A = π • r2
= π • (3)2
= 9π
= 9π • 2
= 18π
Subtract the two areas.
= 72 – 18π