This applet shows one image reflected across one reflection line.

The pre-image is located so that the bottom corners are at point A and B. What are the coordinates of points A and B? Drag the line to different positions and observe the reflected image.
Move the reflection line so that it is on the x-axis. What happens to the image? What are the new coordinates for A' and B' (the images of points A and B)?
Move the reflection line so that it is on the y-axis. What are the new coordinates of A' and B'?