Finding the perimeter of a rectilinear shape

Learning focus

Learn how to find the perimeter of a rectilinear shape.

This includes:

  • a quiz
  • a learning summary
  • one video
  • one activity

Quiz

To get started, let's see how well you know this topic already. Take the quiz below to find out.

Learn

A rectilinear shape is a shape that has straight sides and right angles. It can look like two rectangles that have been joined together.

This shape looks much more complicated than a rectangle, but the method of working out the perimeter is exactly the same.

Add together the lengths of all the sides to find it.

2 + 2 + 3 + 3 + 5 + 5 = 20

The perimeter is 20 cm

Finding the unknown sides

Watch the video below from BBC Bitesize on finding the perimeter of a rectilinear shape when you don't know the length of every side.

Example 1

Can you find the perimeter of this shape?

Step 1. A rectilinear shape. Sides show 15cm, 6cm, 8cm and 3cm.

First, you need to work out the lengths of the missing sides. Let’s focus on the horizontal lines first.

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Example 2

Work out the missing lengths of this shape to find the perimeter.

Step 1. A rectilinear shape. Sides show 7cm, 2cm, 6cm and 12cm.

To begin, let's look at the missing horizontal length.

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Practise

Activity

Make a shape

Cut out 12 squares of paper of equal size or use 12 square sticky notes (you may have these from yesterday's activity). Arrange them into a rectilinear shape.

What is the perimeter of this shape?

Now rearrange the pieces of paper into a new shape. How many different shapes can you make and find the perimeter of?

Play

Play Guardians: Defenders of Mathematica to learn more and sharpen your skills on this topic.

Guardians: Defenders of Mathematica

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