Notice:
and are the endpointsof a diameter.The rotationis the sameas a “reflectionin the origin.”A rotationis an isometry. The imageof a segmentis a congruentsegment.
If is a polygonmatrix,then the matrixfor the imageof the polygonin a rotationis the product
. The LessonExercisesincludeexplorationof this matrixfor a rotation.
90° Rotation
The next exampleis a rotationthroughan angleof.