A regular nonagon can be constructed using a compass and a marked ruler ( or Geogebra tools that simulate a compass and a marked ruler in my case)
This type of construction is not limited to the nonagon , the though behind it can be applied to to all 6n+3 polygons (not the triangle) , I am pretty sure.
Using the hexagon as a base we have a line of 2 across the middle of the hexagon.
Taking this measurement we can now find the height of the nonagon.
A 15-gon construction following the same method
and using the decagon as a base will look like:
