Editing 9 (section)

=== Geometry ===

A [[polygon]] with nine sides is called a [[nonagon]].<ref>Robert Dixon, ''Mathographics''. New York: Courier Dover Publications: 24</ref> A regular nonagon can be [[Constructible polygon|constructed]] with a regular [[compass]], [[straightedge]], and [[angle trisector]].<ref>{{Cite journal|last=Gleason |first=Andrew M. |author-link=Andrew M. Gleason |url=https://www.tandfonline.com/doi/abs/10.1080/00029890.1988.11971989?journalCode=uamm20 |title=Angle trisection, the heptagon, and the triskaidecagon |journal=[[American Mathematical Monthly]] |volume= 95 |issue=3 |year= 1988 |publisher=[[Taylor & Francis, Ltd]] |pages=191–194 |doi=10.2307/2323624 |mr=935432 |jstor=2323624 |s2cid=119831032 }}</ref>

The lowest number of [[square]]s needed for a [[Rectangle#Squared, perfect, and other tiled rectangles|perfect tiling]] of a [[rectangle]] is 9.<ref>{{cite OEIS|A219766|Number of nonsquare simple perfect squared rectangles of order n up to symmetry}}</ref>

9 is the largest single-digit number in the [[decimal|decimal system]].