Year 4 - Maths
Diagonal lines of symmetry
Properties of 2D and 3D shapes and symmetry
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This pupil-friendly study guide includes a unit summary, clear notes, common mistakes, and quick questions with answers.
Unit Summary
In this unit pupils will complete and compose symmetrical shapes from two congruent shapes and investigate lines of symmetry in 2D shapes.
Lesson Summary
You will learn to reflect shaded squares and polygons in a diagonal line of symmetry.
Key Notes
- A line of symmetry does not have to be vertical or horizontal. You can reflect shapes in a diagonal line of symmetry.
- You can reflect a shape by counting the position of each vertex and making a mark, and then joining the marks.
- Each vertex of a shape will be the same distance from the line of symmetry when it is reflected.
Vocabulary To Learn
- Line of symmetry: If you were to fold a shape on its line of symmetry, both halves would match exactly.
- Mirror line: Mirror line is another term to describe the line of symmetry.
- Reflect: When you reflect a shape, you flip it over a mirror line or line of symmetry without turning it or changing the size.
- Reflection: The reflection of a shape is the mirror image of a shape.
Common Mistakes To Avoid
- Children may try to reflect in a diagonal line but not at a 45 degree angle, leading to inaccuracies when marking each vertex.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
A line of symmetry does not have to be vertical or horizontal. You can reflect shapes in a diagonal line of symmetry. You can reflect a shape by counting the position of each vertex and making a mark, and then joining the marks.
2. Use this key word in a maths sentence and explain it clearly. 'Line of symmetry'
If you were to fold a shape on its line of symmetry, both halves would match exactly. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: Children may try to reflect in a diagonal line but not at a 45 degree angle, leading to inaccuracies when marking each vertex. Correction: Encourage children to work horizontally and then vertically, rather than trying to reflect in a diagonal line. Explore how this can be done in either order, orienting the paper, and notice how the same point will still be marked on the grid.
More Lessons In This Unit
- Complete a symmetrical pattern Study Guide
- Explore symmetry by joining two identical shapes Study Guide
- Explore, sort and classify triangles Study Guide
- Find lines of symmetry in 2D shapes Study Guide
- Identify different types of triangle Study Guide
- Investigate lines of symmetry in 2D shapes by folding Study Guide
- Investigate symmetry and symmetrical patterns Study Guide
- Reflect polygons in a line of symmetry Study Guide
- Reflect polygons that are dissected by the line of symmetry Study Guide
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