Diagonal lines of symmetry | Maths | Quizalize & Oak National Academy

Starter quiz

Which of these images shows a correct reflection?
- a)
- b)
- c) ✓
Which of these images is not a correct reflection?
- a)
- b) ✓
- c)
Before reflection, this shape was a trapezium. Now, it is a __________.
- octagon
- hexagon ✓
- pentagon
Before reflection, this shape was a right-angled triangle. Now, it is __________.
- an equilateral triangle
- an isosceles triangle ✓
- a scalene triangle
Here are triangles that have been reflected with one of the sides touching the line of symmetry. Name the shapes that have been made.
- a)
  
  ⇔
  
  triangle ✓
- b)
  
  ⇔
  
  kite ✓
- c)
  
  ⇔
  
  parallelogram ✓
True or false. When you reflect a square that has a side that touches the mirror line, it will create a larger square.
- True
- False ✓

Exit quiz

Match each mirror line with its correct direction.
- a)
  
  ⇔
  
  horizontal ✓
- b)
  
  ⇔
  
  vertical ✓
- c)
  
  ⇔
  
  diagonal ✓
Which image shows a correct reflection?
- a)
- b)
- c) ✓
True or false. This shape has been correctly reflected in a diagonal line of symmetry.
- True ✓
- False
Which image shows a correct reflection?
- a)
- b) ✓
- c)
Here are quadrilaterals that have been reflected with one of the sides touching the line of symmetry. Name the shapes that have been made.
- a)
  
  ⇔
  
  kite ✓
- b)
  
  ⇔
  
  trapezium ✓
- c)
  
  ⇔
  
  rectangle ✓
This shape has been reflected in a diagonal line of symmetry. The new shape is __________.
- an octagon ✓
- a hexagon
- a quadrilateral

Worksheet

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Presentation

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Lesson Details

Key learning points

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.

Common misconception

Children may try to reflect in a diagonal line but not at a 45 degree angle, leading to inaccuracies when marking each vertex.

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.

Keywords

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.