Exploring rotation

Use this sketch to play around with rotation. You can move the blue points, and select what is displayed, and what is hidden.[br][br]Questions:[br][br]For 90 degree and 180 degree rotations, can you predict what will happen to the image when you move a) the source, and b) the centre of rotation?[br][br]Is there any way to figure out where the centre of rotation is, if it is hidden?

Describing Transformations[br][br]Rotation - centre, angle & direction (clockwise or anti-clockwise)[br]Reflection - the line of reflection[br]Enlargement - centre & scale factor[br]Translation - vector