Constructing the midpoint of a segment

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Constructing the midpoint of a segment is probably easier than any other straightedge construction.

Step #1:

Use a ruler and a pencil to construct a segment of any length on a piece of paper as you see it below

Bisecting a segment

Then, fix your compass opening to a distance somewhat bigger than 1/2 the length of segment AB.

You should open your compass large enough, but make sure that the distance is not more than the length of AB.

Step #2:

Put the needle of your compass at A and draw an arc.
Bisecting a segment: step 1
Put the needle of your compass at B and draw an arc.

Bisecting a segment: step 2

The two arcs should meet as shown below:

Bisecting a segment: step 3


Step #3:

Draw a line joining the two points where the two arcs intersect.

Bisecting a segment: step 4


The point of intersection of the line and the segment shown with a green point is your midpoint

Bisecting a segment: step 5