Final answer:
The midpoints of line segments which map preimage points onto mapped image points in a reflection lie on the line of reflection.
Step-by-step explanation:
The midpoints of line segments which map preimage points onto mapped image points in a reflection in the plane lie on the line of reflection. When an object or shape is reflected across a line, the line of reflection acts as a mirror. The preimage and the image are symmetrical across the line of reflection. This means that for each point on the preimage, its corresponding point on the image is directly opposite and equidistant from the line of reflection. As a result, the line drawn from the preimage point to its image point is bisected perpendicularly by the line of reflection.