The distances of the reflected shape and the original shape remain the same from point to point.
No matter where are vertex is, the angles of both shapes are still equal.
When animated, the distances between AD and A'D remain the same.All the distances in pairs (eg AD and A'D) are all the same.
Angles are invariant 
under a reflection.The lengths of the sides of an object are invariant under a reflection.
Points on the mirror line are invariant under a reflection.
I have found that all angles and all distances and measurements were invariant between original shapes and reflected shapes everything was the same except that the shape was reversed.
