5.2.2

Rotations

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Describing Transformations

Transformation can be used to describe how a shape or point moves on coordinate axes.

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Object and image

  • The original shape or point before a transformation is known as the object.
  • The new shape or point after a transformation is known as the image.
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Describing a rotation

  • An angle of rotation and a centre of rotation are required to describe a rotation.
    • The angle of rotation tells you how much the object rotates by.
    • You can often tell the angle of rotation by comparing the orientation (way round) of the object and image.
    • The centre of rotation tells you where the rotation centres around.
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Angle of rotation

  • Look at the orientation to work out the angle of rotation.
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Centre of rotation

  • Find the centre of rotation using tracing paper.
  • Draw around the object and place your pencil where you think the centre of rotation is.
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Centre of rotation cont.

  • Use trial and error until you rotate the object on the tracing paper and it makes the image.
  • This takes a lot of practice to get good at but it gets easier the more you try it.

Rotations

Using x and y coordinates, we can rotate shapes on a graph.

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90o rotation

  • Shape A has rotated 90o anti-clockwise to become shape B, with its centre of rotation at the origin.
    • The x and y coordinates for shape A and B swapped.
    • The x coordinates have changed sign but the y coordinates have not.
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180o rotation

  • Shape A has rotated 180o anti-clockwise to become shape B, with its centre of rotation at the origin.
    • The x and y coordinates for shape A and B are the same but have changed sign.
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270o rotation

  • Shape A has rotated 270o clockwise to become shape B, with its centre of rotation at the origin.
    • The x and y coordinates for shape A and B swapped.
    • The y coordinates have changed sign but the x coordinates have not.
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Clockwise and Anti-clockwise

  • A positive angle of rotation is defined as the angle of rotation in an anti-clockwise direction
  • A negative angle of rotation is defined as the angle of rotation in a clockwise direction.

Jump to other topics

1Numbers

2Equations, Formulae & Identities

3Sequences, Functions & Graphs

4Geometry

5Vectors & Transformation Geometry

6Statistics & Probability

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