Year 9 - Maths
Rotational symmetry
Geometrical properties: similarity and Pythagoras' theorem
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This pupil-friendly study guide includes a unit summary, clear notes, common mistakes, and quick questions with answers.
Unit Summary
This unit explores the concepts of congruence and similarity, and ways to prove or disprove similarity between shapes. We then explore further properties of triangles with Pythagoras' Theorem.
Lesson Summary
You will learn to recognise rotational symmetry in shapes.
Key Notes
- Congruent shapes can be used to investigate rotational symmetry.
- The centre of rotation is the centre of the shape.
- You must be careful not to count the starting point twice.
Vocabulary To Learn
- Rotational symmetry: Rotational symmetry describes when a shape appears the same after some rotation. The order of rotational symmetry is the number of times the image appears the same as the object in one full turn.
Common Mistakes To Avoid
- When rotating a shape to count its order of rotational symmetry, pupils may count the starting position twice: once at the start and then again at the end of the full turn.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
Congruent shapes can be used to investigate rotational symmetry. The centre of rotation is the centre of the shape.
2. Use this key word in a maths sentence and explain it clearly. 'Rotational symmetry'
Rotational symmetry describes when a shape appears the same after some rotation. The order of rotational symmetry is the number of times the image appears the same as the object in one full turn. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: When rotating a shape to count its order of rotational symmetry, pupils may count the starting position twice: once at the start and then again at the end of the full turn. Correction: Encourage pupils to be consistent with when they count the starting position, either always counting it before they begin rotating the shape or always counting it at the end of the full turn.
More Lessons In This Unit
- Applying the criteria for congruence Study Guide
- Checking understanding of congruence Study Guide
- Checking understanding of similarity Study Guide
- Congruence in shapes Study Guide
- Congruent triangles (ASA and AAS) Study Guide
- Congruent triangles (RHS) Study Guide
- Congruent triangles (SAS) Study Guide
- Congruent triangles (SSS) Study Guide
- Congruent, similar or neither Study Guide
- Demonstrating Pythagoras' theorem Study Guide
- Determining which side Study Guide
- Further demonstrating of Pythagoras' theorem Study Guide
- Length of a shorter side Study Guide
- Length of the hypotenuse Study Guide
- Problem solving with similarity and Pythagoras' theorem Study Guide
- Pythagoras' theorem in context Study Guide
- Similarity in shapes Study Guide
Browse all guides in the Year 9 Maths guide library.