Identify right angles

What you will learn

• Identify right angles

Models used: number sentences, stories, diagrams.

Compare the opening with a square corner

This opening is smaller than a square corner.

1. This opening is smaller than a square corner.

   Longer sides do not make a wider opening. A square corner is a useful reference; a protractor measures from the correct baseline.

2. This opening matches a square corner. It is a right angle.

3. This opening is wider than a square corner. It is greater than a right angle.

Worked example: A new example, together

Compare the marked angle with a right angle.

1. Find the vertex and compare the opening, keeping the baseline fixed.

   The amount of turn determines the angle, independent of ray length.

2. Imagine a square corner with a 90° opening.

   Compare the marked angle with a right angle.

   a right angle

3. Imagine a square corner with a 90° opening.

4. Compare with the corner of a square.

5. It is a right angle.

6. Check the result against the question we started with.

   The opening is a right angle.

   We found a right angle. The amount of turn determines the angle, independent of ray length.

Common mistakes to discuss

• A tilted corner is not a right angle. A right angle stays a right angle when the figure is turned. Compare it with the corner of a page in the same position.

Check your understanding

• Identify right angles
• recognise or measure a turn independently of ray length
• check the answer against the original quantities and units

Explain your reasoning to an adult, then try a fresh question in the interactive lesson. A result from one attempt is not proof of lasting mastery.