A visual construction of a regular nonagon with compass and marked ruler (neusis construction of a nonagon).
Start with a hexagon and triangle as a base,
If the side of the hexagon is 1 the bold lines shown in the picture have a value of 2 .
Extend the lines of the triangle . Draw a circle of radius 1 as shown on the perpendicular line. This circle marks 2 points on each of the lines extended from the triangle. Join the points as shown.
Draw circles of radius 1 from the new points to complete the nonagon
