The pre image above was rotated 90 degrees clockwise about the origin (point F). In order for a translation to be considered a rotation, each vertex must move the same degree and direction around the center of rotation. If you were to measure the degree of EFE' and the degree of DFD', they would have the same angle measure, as well as CFC' and so on. Each vertex on the image is the same distance from the point of rotation as each vertex on the pre image. For example, if you were to measure line segments FD and FD', you would find that they are the same length. This applies to all of the corresponding vertices on each of the figures.