Ever thought of constructing a 4 units long segment, given the unit length?[br][br]Here is another method: Construct a regular 10-gon with unit sides, and draw some diagonals and lengthen a side of it as shown in the figure. Then, by joining some intersection points being created, some 4 units long segments will also appear.[br][br]This theorem has been automatically obtained by the software tool [url=https://github.com/kovzol/RegularNGons]RegularNGons[/url].