1. Warm Up
Find the area of the following figures.
1. A triangle with a base of 12.4 m and a height of 5 m
2. A parallelogram with a base of 36 in. and a height of 15 in.
3. A square with side lengths of 2.05 yd
31 m2
540 in2
yd2

2. Learn to find the area of irregular figures.

3. Vocabulary
composite figure

4. A composite figure is made up of simple geometric shapes, such as triangles and rectangles. You can find the area of an irregular figure by separating it into non- overlapping familiar figures. The sum of the areas of these figures is the area of the irregular figure. You can also estimate the area of an irregular figure by using graph paper.

5. Additional Example 1: Estimating the Area of an Irregular Figure
Estimate the area of the figure. Each square represents one square yard.
Count the number of filled or almost-filled squares: 45 squares.
Count the number of squares that are about half-full: 10 squares.
Add the number of filled squares plus ½ the number of half-filled
squares: 45 + ( • 10) = =50
1 2
The area of the figure is about 50 yd2.

6. Count the number of filled or almost-filled squares: 11 red squares.
Check It Out: Example 1
Estimate the area of the figure. Each square represents one square yard.
Count the number of filled or almost-filled squares: 11 red squares.
Count the number of squares that are about half-full: 8 green squares.
Add the number of filled squares plus ½ the number of half-filled
squares: 11 + ( • 8) = =15.
1 2
The area of the figure is about 15 yd . 2

7. Additional Example 2: Finding the Area of an Irregular Figure
Find the area of the irregular figure. Use for .
Step 1: Separate the figure into smaller, familiar figures.
16 m
Step 2: Find the area of each smaller figure.
9 m
Area of the parallelogram:
16 m
A = bh
Use the formula for the area of a parallelogram.
A = 16 • 9
Substitute 16 for b.
Substitute 9 for h.
A = 144

8. Additional Example 2 Continued
Find the area of the irregular figure. Use for .
16 m
Area of the semicircle:
9 m
The area of a semicircle
is the area of a circle.
1 2
A = (r)‏ 1 2 __
16 m
A ≈ (3.14 • 82)‏ 1 2 __
Substitute 3.14 for  and 8 for r.
A ≈ (200.96) 1 2 __
A ≈
Multiply.

9. Additional Example 2 Continued
Find the area of the irregular figure. Use for .
Step 3: Add the area to find the total area.
16 m
9 m
A ≈ =
16 m
The area of the figure is about m2.

10. Find the area of the irregular figure. Use 3.14 for .
Check It Out: Example 2
Find the area of the irregular figure. Use for .
Step 1: Separate the figure into smaller, familiar figures.
8 yd
Step 2: Find the area of each smaller figure.
9 yd
9 yd
Area of the rectangle:
A = lw
Use the formula for the area of a rectangle.
3 yd
A = 8 • 9
Substitute 8 for l.
Substitute 9 for w.
A = 72

11. Check It Out: Example 2 Continued
Find the area of the irregular figure. Use for .
Area of the triangle:
8 yd
9 yd
The area of a triangle
is the b • h.
1 2
A = bh 1 2 __
9 yd
A = (2 • 9)‏ 1 2 __
Substitute 2 for b and 9 for h.
2 yd
A = (18) 1 2 __
A = 9
Multiply.

12. Check It Out: Example 2 Continued
Find the area of the irregular figure. Use for .
Step 3: Add the area to find the total area.
A = = 81
The area of the figure is about 81 yd2.

13. Check It Out: Example 3
The Franklins want to wallpaper the wall of their daughters loft. How much wallpaper will they need?
6 ft
23 ft
18 ft
5 ft

14. Check It Out: Example 3 Continued
Solve 3
Find the area of each smaller figure.
Area of the rectangle:
Area of the triangle:
A = lw
A = bh 1 2 __
A = 18 • 6
A = (5 • 11)‏ 1 2 __
A = 108
A = (55)‏ 1 2 __
Add the areas to find the total area.
A = 27.5
A = = 135.5
The Franklins need ft2 of wallpaper.

15. Lesson Quiz
Find the perimeter and area of each figure. 1. 2.
31.42 cm, cm2
39.1 ft, 84 ft2