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This section will cover the fundamentals and rules for finding the perimeter.
Finding the Perimeter of Quadrilaterals
Perimeter is the total distance around a figure. Finding the perimeter is like finding the amount of aluminum siding it will take to cover the outside of a house.
A square is a plane figure that has four sides that are equal. As a shortcut, you can multiply the distance of all sides by four.
The formula for the perimeter of a square is:
Perimeter = 4 x side
Example 1: Find the perimeter of the square.
Perimeter = 4 x side
Perimeter = 4 x 3
Perimeter = 12 in.
The formula for the perimeter of a rectangle is:
Perimeter = 2 x length + 2 x width
Example 2: Find the perimeter of the rectangle.
Perimeter = 2 x length + 2 x width
Perimeter = 2 x 6 + 2 x 3
Perimeter = 12 + 6
Perimeter = 18 in.
Finding the Perimeter of Polygons
The formula for the perimeter of a triangle is:
Example 1: Find the perimeter of the triangle.
Perimeter = 6 + 8 + 4
Perimeter = 18 in.
Example 2: Suppose you have the perimeter and width of a rectangle, and you were told to find the length. How would you find it?
Plug the information you already have into the formula. Then solve for length.
Perimeter = 2 x length + 2 x width
30 = 2 x length + 2 x 5
30 = 2 x length + 10
- 10 = -10
20 = 2 x length
2 2
10 feet = length
Perimeter = 2 x length + 2 x width
30 = 2 x 10 + 2 x 5
30 = 20 + 10
30 = 30
The answer is correct.
Check your work:
Example 3: Let's say you wanted to find the perimeter of the polygon shown below, but you were only given part of the measurements.
To find the measurements of the sides that are not given, subtract the measurements of the sides that are given.
We'll label one side, Side A, and the other side, Side B.
Side B = 8 in. - 2 in.
Side B = 6 in.
Side A = 5 in. - 3 in.
Side A = 2 in.
Choose a starting point, and add all the sides together.
8 + 3 + 6 + 2 + 2 + 5 = 26 inches.
Geometry is a type of math that focuses on the study of shapes and measurements and relations to points, lines, angles, surfaces, and solids.
Math: Perimeter - Tutorial
