课 17, 主题 3

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Rotational-Symmetry Edexcel Foundation

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Exam code:1MA1

Rotational symmetry

What is the order of rotational symmetry?

Rotational symmetry refers to the number of times a shape looks the same as it is rotated 360° about its centre
This number is called the order of rotational symmetry
Tracing paper can help work out the order of rotational symmetry
- Draw an arrow on the tracing paper so you can easily tell when you have turned it through 360°

finding the order of rotational symmetry using tracing paper

finding the order of rotational symmetry using tracing paper 2

finding the order of rotational symmetry using tracing paper 3

Notice that returning to the original shape contributes 1 to the order
- This means a shape can never have order 0
- A shape with rotational symmetry order 1 may be described as not having any rotational symmetry
- The only time it looks the same is when you get back to the start

Examiner Tips and Tricks

Remember to use the trick above; using an upwards arrow on the tracing paper to show the starting orientation of the shape.

Worked Example

For the shape below, shade exactly 4 more squares so that the shape has rotational symmetry of order 4.

3-1-line-and-rotation-symmetry-we

The shape below appears the same 4 times if rotated through 360 degrees

3-1-1-rotation-symmetry-we-answer

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