Perimeter: find the missing side lengths
Key Notes :
The perimeter of a shape is the distance around the shape. It is the total length of the shape’s sides.
Identify the Shape: Determine the type of shape for which you need to find the missing side lengths. Common shapes include squares, rectangles, triangles, and irregular polygons
Given Information: Look at the information provided in the problem. Identify which sides are given (with lengths) and which sides are missing.
Use the Perimeter Formula: Recall the formula for perimeter of the specific shape:
- Square: Perimeter = 4 × side length
- Rectangle: Perimeter = 2 × (length + width)
- Triangle: Perimeter = sum of the lengths of all three sides
- Irregular Polygon: Perimeter = sum of the lengths of all sides
- Solve for the Missing Side Length: Once you have set up the equation or identified the relationship between given and missing sides, solve for the missing side length using basic arithmetic operations (addition, subtraction, multiplication, division)
Learn with an example
▶️ The perimeter of the shape is 16 units. What is the value of z?
z =____ units
The perimeter of the shape is 16 units. The length of one side is missing.
To find the missing side length, write an equation for the perimeter of the shape. The perimeter of a shape equals the sum of all of its side lengths.
3 + 3 + 3 + z + 3 = perimeter
The perimeter is 16 units.
3 + 3 + 3 + z + 3 = 16
Add the lengths of the sides you know.
12 + z = 16
Find the side length that makes the equation true.
12 + 4 = 16
The value of z is 4 units.
z=4 units
▶️ The perimeter of the shape is 16 units. What is the value of z?
z = ____ units
The perimeter of the shape is 16 units. The length of one side is missing.
To find the missing side length, write an equation for the perimeter of the shape. The perimeter of a shape equals the sum of all of its side lengths.
3 + 3 + 3 + z + 3 = perimeter
The perimeter is 16 units.
3 + 3 + 3 + z + 3 = 16
Add the lengths of the sides you know.
12 + z = 16
Find the side length that makes the equation true.
12 + 4 = 16
The value of z is 4 units.
z = 4 units
▶️ The perimeter of the triangle is 16 units. What is the value of z?
z = ____ units
The perimeter of the triangle is 16 units. The length of one side is missing.
To find the missing side length, write an equation for the perimeter of the triangle. The perimeter of a triangle equals the sum of all of its side lengths.
6 + 6 + z = perimeter
The perimeter is 16 units.
6 + 6 + z = 16
Add the lengths of the sides you know.
12 + z = 16
Find the side length that makes the equation true.
12 + 4 = 16
The value of z is 4 units.
z = 4 units
Let’s practice!🖊️
