Construction #4
Bisect a Segment
Perpendicular Bisector of a Segment
Find the midpoint of a segment
Divide a segment into 2 congruent segments
To see a video of Mr. Ochs doing examples
Mr Ochs Video To see and example done in flash click on a link below Math Open Ref Math is Fun 

Given a segment, construct the perpendicular bisector of the segment.
Construct the perpendicular bisector of segment BC.
1) Choose a radius for the compass that is larger than ½ the segment.
2) With this radius place your compass pointer on one endpoint of the segment and strike a semicircle(1/2 circle) that passes through the segment.
3) Keeping the same radius, repeat step 2 with the pointer on the other endpoint of the segment. The two semicircles will intersect.
Note: Eventually the semicircles can be reduced to two small arcs on either side of the segment.
4) With a straight edge draw a line through the points of intersection created by the arcs in steps 2 and 3.
Note 2 : This is how we find the midpoint of a segment.
Construct the perpendicular bisector of segment BC.
1) Choose a radius for the compass that is larger than ½ the segment.
2) With this radius place your compass pointer on one endpoint of the segment and strike a semicircle(1/2 circle) that passes through the segment.
3) Keeping the same radius, repeat step 2 with the pointer on the other endpoint of the segment. The two semicircles will intersect.
Note: Eventually the semicircles can be reduced to two small arcs on either side of the segment.
4) With a straight edge draw a line through the points of intersection created by the arcs in steps 2 and 3.
Note 2 : This is how we find the midpoint of a segment.