We will discuss here about reflection of a point in a line.
The reflection of the point (object) P in the line AB is the point P’ such that
(i) PP’ ⊥ AB, and (ii) AB bisect PP’, i.e., PQ = QP’
P’ is called the image of the point P in the line AB, called axis of reflection. We also say that on reflection in the line AB, the point P is mapped onto P’.
Clearly, AB is the perpendicular bisector of the line segment PP’, and P and P’ are on the opposite sides of AB.