The correct diagram is attached.
Explanation:
Using technology (such as Geogebra), first construct a line segment. Name the endpoints C and D.
Construct the perpendicular bisector of this segment. Label the intersection point with CD as B, and create another point A above it.
Measure the distance from C to B and from B to D. They will be the same.
Measure the distance from A to B. If it is not the same as that from C to B, slide A along line AB until the distance is the same.
Using a compass and straightedge:
First construct segment CD, being sure to label the endpoints.
Set your compass a little more than halfway from C to D. With your compass set on C, draw an arc above segment CD.
With your compass set on D (the same distance as before) draw an arc above segment CD to intersect your first arc. Mark this intersection point as E.
Connect E to CD using a straightedge; mark the intersection point as B.
Set your compass the distance from C to B. With your compass on B, mark an arc on EB. Mark this intersection point as A.
AB will be the same distance as CB and BD.
