Transformations - Rotation

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?

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