Consider the following construction.

Given a line segment AB. Construct a perpendicular segment BD such that 2BD = AB. Draw AD. Mark point E on AD such that DE = DB. Mark point F on AB such that AE = AF

Given a line segment AB.

Construct a perpendicular segment BD such that 2BD = AB.

Draw AD.

Mark point E on AD such that DE = DB.

Mark point F on AB such that AE = AF