Coordinate Rules for Rotations

In general, we can state the following coordinate rules for (counterclockwise) rotations about the origin:

For a rotation of 90^o:  (x, y) --> (–y, x)

For a rotation of 180^o:  (x, y) --> (–x, –y)

For a rotation of 270^o:  (x, y) --> (y, –x)

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