Formally Defining Reflections A reflection is a transformation such that:
•The line of reflection is the perpendicular (bisector) of the line segment connecting a point in the pre-image with its corresponding image.

This tells us that:
Line segment BB' is perpendicular
to the line of reflection.

Point L is the (Bisector)
of line segment BB'.

Point L is equidistant from B and B'.

Line segments BB' and AA' are (Parallel)