One of the properties of a shape that is measured is its perimeter. This is the distance around the edge of a shape. For a shape with straight edges, you can work out the perimeter by measuring the length of each edge and then adding these together.
For example, one practical application of this would be someone wanting to decorate the room shown in Figure 12, using a border along the top of all the walls. To determine the length of the border they would need to work out the perimeter. So the border would measure:
An alternative way to calculate this would be to note that the pairs of sides are the same length, giving us:
Have a go yourself in this next activity.
Activity _unit7.2.1 Activity 2 Around the edge
- a.This figure is formed from three of the shapes. What is its perimeter?
a.Starting on the left at the top of shape 3 and going clockwise around the figure, the perimeter is:
You could have also shown the working as:
When a shape has straight sides, you can measure the perimeter fairly easily by considering each side in turn. However, measuring lines that are not straight can be more difficult. If you need the measurement for some practical purpose, then you can use a piece of string to wrap around an object and then measure the string. However, as you’ll discover in the next section there more precise methods to calculate these in maths.