May 12, 2013 ... 2 cm. Finding Perimeter and Area of Irregular Figures. Notes/Practice. Perimeter
Notes. Sample 1. To find the perimeter of an irregular figure:.
Grade 5 Mathematics Unit: 09 Lesson: 03
Finding Perimeter and Area of Irregular Figures Notes/Practice Perimeter Notes Sample 1 To find the perimeter of an irregular figure: •
2.6 cm
Add all the side lengths.
2.5 cm
2.6 + 2.5 + 2 + 3.3 + 1.6 = 12
The perimeter is 12 cm.
1.6 cm
2 cm 3.3 cm
Sample 2 To find the length of an unknown side of an irregular figure when the perimeter is known: •
Find the length of side x if the perimeter of the figure equals 50 feet.
x
P = sum of the side lengths 50 = x + 16 + 6 + 4 + 19 50 = x + 45 50 – 45 = x x = 5; because 45 + 5 = 50
Finding Perimeter of Irregular Figures Notes/Practice Perimeter and Area Notes Sample
15 in.
Find the perimeter and area of this polygon. 7 in. 5 in.
11 in.
4 in.
? •
First, find the unknown side length.
•
Look at the sides opposite the unknown side. Their measures are 15 in. and 5 in. The unknown side is 15 + 5 or 20 inches long.
15 in. 7 in. 5 in.
Find the perimeter using the sum of the side lengths.
11 in.
4 in.
P = 4 + 5 + 7 + 15 + 11 + 20 = 62 in.
5 in. + 15 in. = 20 in.
•
15 in.
The area of this figure can be found by calculating the area of the small rectangle and adding it to the large rectangle. A = (4 x 5) + (15 x 11) = 185 in
Finding Perimeter and Area of Irregular Figures Notes/Practice Practice: Use the figure itself and the space next to each figure to show your work and explain your reasoning. (1) Find the perimeter of this figure.
13 m 45 m 24 m
43 m (2)
What is the length of side x if the perimeter of this figure equals 941 mm?
