DIAGRAM OF A NONAGON

The nonagon tracing (9 sides, 9 angles at the centre 40°) comes down to making the angle trisection centered at 120°, this angle is achieved by making an inscribed equilateral triangle with only the use of a ruler and a compass.

• Create a circle centered at O, of radius OX, with an angle OÂB = 120° (AB being one of the inscribed equilateral triangle sides)
• Create an arc of circle of radius XY centered at X
• Create an arc of circle of radius YX centered at Y
  
  These arcs intersect at I
  
  
• Draw IA and IB that intersect the diameter XY
  at C and D
• From C on any straight line trace with the compass three equal segments CE = EF = FG
• Join GD and trace the parallels (with the ruler and compass), FH and EK that intersect XY at K and H.
• Draw IK and IH that intersect XY at K and H
• Draw IK and IH that intersect the circle at L and M
• The arcs AL, LM, MB are equals with angles centered at 40°

Following page: the Golden Number