# 9.03 Perimeter

Lesson

## Ideas

Can you find the  perimeter  of this polygon?

### Examples

#### Example 1

Find the perimeter of the figure shown.

Worked Solution
Create a strategy

Add all the lengths of the sides to find the perimeter.

Apply the idea
Idea summary

Remember that perimeter is the distance around the entire shape.

It doesn't matter what shape our polygon is, as long as we add the length of every side, we can work out the perimeter.

We must also write the unit of measurement with our answers, such as \text{cm, m, mm}, or \text{km}.

## Perimeter of rectangles

Rectangles are a special kind of polygon, and they have special features that we can use to work out the perimeter. With two pairs of equal sides, we can work out the perimeter by adding the length and width and doubling it.

### Examples

#### Example 2

Find the perimeter of the rectangle shown.

Worked Solution
Create a strategy

The perimeter of a rectangle can be found using the formula:\text{Perimeter} = 2 \times ( \text{length} + \text{width})

Apply the idea
Idea summary

The perimeter of a rectangle can be found using the formula:\text{Perimeter} = 2 \times ( \text{length} + \text{width})

## Perimeter of triangles

Perimeter is all about the distance around the outside of our shape, so the perimeter of a triangle means adding 3 sides together. We can calculate the perimeter of equilateral, isosceles and scalene triangles, using what we know about those triangles, to help with missing values.

Let's see what features each of those triangles have, and how it can help us work out the perimeter of the triangle.

### Examples

#### Example 3

Find the perimeter of an equilateral triangle with a side length of 5 mm.

Worked Solution
Create a strategy

An equilateral triangle has all three sides (s) equal, so we can found the perimeter using this formula: \text{ Perimeter} = 3 \times \text{s}

Apply the idea
Idea summary

Different kinds of shapes mean we don't always need to know how long each side is to work out the perimeter. Using the features of the shapes can help us with missing values.

### Outcomes

#### VCMMG224

Solve problems involving the comparison of lengths and areas using appropriate units.