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Rotational Symmetry

M6G1b – Investigate rotational symmetry, including degree of rotation.

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Vocabulary

1) Rotate – to turn a figure around a fixed point

2) Point of rotation - the point around which a figure is rotated (a.k.a. the center of rotation)

3) Rotational Symmetry – when a figure fits exactly on top of itself after a rotation of 180° or less4) Angle of rotation – the smallest angle a figure can be rotated to look exactly the same

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A square has rotational symmetry.

• The smallest angle a figure can be rotated and still look the same is called the angle of rotation.

• What is the angle of rotation of a square? 90°

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Does a rectangle have rotational symmetry?

What is the degree of rotation? 180°

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Does each figure have rotational symmetry?

To find the degree of rotation mathematically, divide ______ by the number of times the pattern _________

360 ÷ 4 = 360 ÷ 3 = 360 ÷ 6 = 90 120 60

360°repeats.

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Do these figures have rotational symmetry?

Yes - 72°

NO

NO

Yes - 45°

Yes - 180°

Yes - 90°

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Rotational Symmetry in the AlphabetWhich letters have rotational symmetry?

For those with rotational symmetry, what is the degree of rotation?

A B C D E F G H I

J K L M N O P Q R

S T U V W X Y Z

180° 180° 180°

180° 180° 180°

180°

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Rotational Symmetry all around usWhich road signs have rotational symmetry?

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Rotational Symmetry all around us

120° 180° 180°

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Rotational Symmetry all around us

90° 120° 180°

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Rotational Symmetry all around us

120° 180°