ANGLE TRISECTION

The so-called THALES method used by the companions (historical craftsmen).

Let AÔB be an angle

Create a circle centered at O radius OB diameter CB

Create an arc of circle centered at B radius BC

Create an arc of circle centered at C radius CB

These arcs cross at D

Draw AD that crosses OB at E

On any straight line trace 3 equal segments EG, GH, HI

Draw BI and parallels to BI passing through H and G and crossing EB at J and K

Draw DJ and DK crossing the circle centered at O at N and M

The arcs BM, MN and NA are equals

So AÔN = NÔM = MÔB

Following page: the nonagon drawing