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Year 4

Reflect polygons in a line of symmetry

I can reflect polygons in a line of symmetry, including when there are no sides parallel to the line of symmetry.

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New
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Year 4

Reflect polygons in a line of symmetry

I can reflect polygons in a line of symmetry, including when there are no sides parallel to the line of symmetry.

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Lesson details

Key learning points

  1. When you reflect a shape, it will be the same distance from the mirror line on both sides.
  2. You can reflect a shape by counting the position of each vertex and making a mark, and then joining the marks.

Keywords

  • Line of symmetry - If you were to fold a shape on its line of symmetry, both halves would match exactly.

  • Mirror line - Another term for a line of symmetry. If you were to fold a shape on its line of symmetry, both halves would match exactly.

  • 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 mirror image of a shape.

Common misconception

Children may translate or copy a shape rather than 'flipping it' over the line of symmetry.

Use mirrors to support children's understanding of how a shape flips when it is reflected. Explore this idea with a wide variety of shapes.

Although children are taught different strategies to reflect shapes in this lesson, they may benefit from using a mirror to support their understanding of reflective symmetry.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
Which of these shapes are regular polygons?
Correct answer: Equilateral triangle
Rectangle
Correct answer: Square
Trapezium
Q2.
An equilateral triangle has ___ lines of symmetry.
0
1
2
Correct answer: 3
Q3.
This shape is a regular pentagon. It has lines of symmetry.
An image in a quiz
Correct Answer: 5
Q4.
The number of lines of symmetry in a __________ is equal to the number of sides.
quadrilateral
triangle
Correct answer: regular polygon
Q5.
True or false. An isosceles triangle has 3 lines of symmetry.
An image in a quiz
True
Correct answer: False
Q6.
Which statement is true?
Squares and rectangles both have 4 lines of symmetry.
A rectangle has more lines of symmetry than a square.
Correct answer: A square has 4 lines of symmetry, and a rectangle has 2 lines of symmetry.
Squares and rectangles are both regular polygons.

Exit quiz

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6 Questions

Q1.
The mirror image of a shape is a __________ of it.
Correct answer: reflection
larger shape
smaller shape
Q2.
Which image shows a reflection?
a)
Correct answer: b)
c)
Q3.
True or false. This image shows a reflection.
An image in a quiz
True
Correct answer: False
Q4.
Which image shows a reflection?
Correct answer: a)
b)
c)
Q5.
Sam is using vertices to reflect this shape. Which vertex has been placed in the wrong position on the grid?
An image in a quiz
a)
Correct answer: b)
c)
Q6.
Complete the sentence. This image does not show a reflection because __________.
An image in a quiz
The 'reflected' shape is a different size.
Correct answer: The 'reflected' shape is not the same distance from the mirror line.
The 'reflected' shape has not been flipped.