(1) The image and preimage triangles overlap when the line of reflection is ON (passes through) the preimage. [br][br](2) One pair of corresponding vertices will be at the same point when the line of reflection passes through that vertex on the preimage. For example, if the line of reflection passes through point A, then point A and A' will be at the same point and overlap.

The line of reflection passes through the midpoint of the line segments AA', BB', and CC'. We can also say that the line of reflection cuts these lines in half. The line of reflection is also perpendicular to AA', BB' and CC". So the line of reflection is the perpendicular bisector of AA', BB', and CC', or any line segment a point on the preimage to its corresponding point on the image.