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Rotations of points, shapes
In math, a rotation lives up to its name!
To rotate an object you need a center of rotation and how much you want to rotate it. By convention, positive rotations go counter clockwise, and negative rotations go clockwise.
Rotation notation is usually denoted R( center , degrees)
- "Center" is the 'center of rotation.' This is the point around which you are performing your mathematical rotation.
- "Degrees" stands for how many degrees you should rotate. A positive number usually by convention means counter clockwise.
Very often rotations are performed using coordinate notation as they all are on this page. The coordinates allow us to easily describe the image and its preimage. Examples of the most common rotations
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1)
Rotation by 90° about the origin: R(origin, 90°)
A rotation by 90° about the origin can be seen in the picture below in which A is rotated to its image A'.
The general rule for a rotation by 90° about the origin is (A,B)  (-B, A)
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2)
Rotation by 180° about the origin: R(origin, 180°)
A rotation by 180° about the origin can be seen in the picture below in which A is rotated to its image A'.
The general rule for a rotation by 180° about the origin is (A,B) (-A, -B)
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3)
Rotation by 270° about the origin: R(origin, 270°)
A rotation by 270° about the origin can be seen in the picture below in which A is rotated to its image A'.
The general rule for a rotation by 270° about the origin is (A,B) (B, -A)
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