Turns the pre-image based on the angle given. you must know the center of rotation and angle of rotation. Rotations are counterclockwise unless told differently.
90 degrees (-y,x)
180 degrees (-x,-y)
270 degrees (y,-x)
This is moving a figure around a fixed point, which may be inside, on the edge, or outside the figure. Movement may be clockwise or counterclockwise.