Transformations - Reflection

Exploring reflection.
Use this sketch to play around with reflection. You can move the blue points, and select what is displayed, and what is hidden.[br][br]Questions:[br][br]Can you predict what will happen to the image when you move a) the source, and b) the mirror line?[br][br]Is there any way to figure out the mirror line if it is hidden?

Information: Transformations - Reflection