This document discusses 2D rotation in computer graphics. It provides the rotation equations to calculate new x- and y-coordinates when an object is rotated by an angle θ. As an example, it solves the problem of rotating a triangle with vertices at (0,0), (1,0), and (1,1) by 90 degrees counterclockwise. The new coordinates of the rotated triangle are found to be (0,0), (0,1), and (-1,1).