Counterclockwise 90° Rotation: Corresponding Points and Polygons

This example demonstrates how to rotate a set of points and a polygon counterclockwise by 90° (CCW), and how the rotated image forms clear correspondences with the original. It highlights key ideas in transformation geometry: rotation as a rigid motion, the meaning of a 90° directed turn, preservation of distances (congruence/equal-length relationships), and the role of the rotation center and orientation. Construction-wise, it uses Polygon to build the initial polygon from points (e.g., A, B, C and related parameters), Intersect to determine intersection points that help verify geometric relationships (e.g., objects like d, e), and Rotate to generate the rotated counterparts about a center O (e.g., A', B', C' and associated auxiliary objects such as a', b', c', t1'). Text labels are added to emphasize matching between pre- and post-rotation objects. Suitable for secondary school geometry, transformation/rigid-motion lessons, and interactive classroom demonstrations or practice.