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Regular nonagon (enneagon)
A regular nonagon (enneagon)
TeepRegular polygon
Edges an vertices9
Schläfli seembol{9}
Coxeter diagram
Symmetry groupDihedral (Dih9), order 2×9
Internal angle (degrees)140°
Dual polygonself
Propertiesconvex, cyclic, equilateral, isogonal, isotoxal

In geometry, a nonagon /ˈnɒnəɡɒn/ (or enneagon /ˈɛnəɡɒn/) 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