Let AB is a line and PQ is perpendicular bisector of AB.
PQ has so many points on it.
Let, C, D are points on it. Now, PQ has four points two end points P and Q and two points C and D.
In figure above,
Point P is equidistant from the end points of the line AB.
PA = PB
Similarly, point C is equidistant from the end points of the line AB.
CA = CB
Similarly, point D is equidistant from the end points of the line AB.
DA = DB
Similarly, point Q is equidistant from the end points of the line AB.
QA = QB
Hence,proved.