Answer: 90 degrees clockwise
This is equivalent to 270 degrees counterclockwise
The rule for either rotation is [tex](x,y) \to (y,-x)[/tex]
The x and y coordinates swap places, and the new second coordinate flips from positive to negative (or vice versa).
The diagram below shows an example of this for the point (-4,-2) rotating to (-2, 4). The center of the rotation is the origin (0,0).
