Lesson 14 — Activity 1: Perimeter of Regular Shapes
Completion requirements
Lesson 14 — Activity 1:
Perimeter
of Regular Shapes
Getting Ready
Perimeter is the distance around the outside of a shape. People use perimeter for a variety of purposes, such as fencing off an area to plant a garden, framing a picture, or putting baseboards on the walls of a room.
Can you think of other examples of using perimeter in your everyday life?
Think about This:
More examples of using perimeter in everyday life include putting a wallpaper border in a room in your house, building a fence around your property, and even planning a swimming pool for the backyard.
Calculating an octagonal window for a housing project involves perimeter.
Finding Perimeter
Perimeter can be determined using grids or geoboards and is calculated using equations called formulas.
Let's look at a grid example first.
Count the number of squares along each of the sides and ADD them together to calculate the perimeter. Each square is one unit.
Perimeter = 6 units + 3 units + 6 units + 3 units = 18 units
Courtesy of ADLC
Let's try finding perimeter using a geoboard.
Count the lengths of all the sides and add them up.
Perimeter = 3 units + 3 units + 3 units + 3 units = 12 units
Courtesy of mathlearningcenter.org/geoboard
Try This:
1. Determine the perimeter of the shape on the grid below.
Perimeter = 7 units + 5 units + 7 units + 5 units = 24 units
Courtesy of ADLC
2. Use a geoboard to make a shape with this perimeter: 8 + 5 + 8 + 5 = 26 units
(You may use a geoboard in your classroom or click here to use a virtual geoboard.
(To use the virtual geoboard, choose the rectangle board for this activity. You will find it by clicking on the rectangle at the bottom of the page.)
To begin, select any colour of elastic and drag it up onto the board by holding down the left mouse key. When you are where you want to place the elastic, release your left mouse key. Move your mouse around and notice the elastic stretches as your mouse moves.
Your shape may look like this:
Courtesy of mathlearningcenter.org/geoboard
Formulas are equations used to make specific calculations.
Below is a table that gives formulas for perimeter.
Courtesy of ADLC
As noted above, there are many instances of using perimeter in our everyday lives. Look at this example:
Courtesy of Pixabay
Let's say you have a job installing doors in homes. You will need to measure around the outside of each door opening (this is the perimeter).
Courtesy of ADLC
You can use the formula for rectangles above to find the perimeter:
You can add:
P = s + s + s + s
P = 3 + 6 + 3 + 6 = 18 ft
OR
You can multiply:
P = 2 x l + 2 x w
P = 2l + 2w
P = 2 x 6 + 2 x 3
P = 12 + 6 = 18 ft
Self-check!
Try This!
Answer the questions regarding perimeter on your own first.
When you are finished, click on the tabs below to check your answers!
Stan wished to measure the opening for a new window in his kitchen. Help Stan find the perimeter, by using one of the formulas for rectangles above.
P = s + s + s + s
P = 2 + 4 + 2 + 4 = 12 units
OR
P = 2l + 2w
P = 2(4) + 2(2) = 12 units
Dan wants to measure for a garden he planned for his backyard. Help Dan find the perimeter, by using the
formula for triangles above.
P = s + s + s
P = 2 + 3 + 5 = 10 units
Courtesy of ADLC