Nonagon - math word definition - Math Open Reference

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Nonagon (9-gon) (also Enneagon)

From Latin: nonus - "ninth"

Definition: A polygon with 9 sides

Try this Adjust the nonagon below by dragging any orange dot. By clicking on the top left command line, you can switch it between a regular and irregular nonagon.

Properties of regular nonagons

Interior angle	140°	Like any regular polygon, to find the interior angle we use the formula (180n–360)/n . For a nonagon, n=9. See Interior Angles of a Polygon
Exterior Angle	40°	To find the exterior angle of a regular decagon, we use the fact that the exterior angle forms a linear pair with the interior angle, so in general it is given by the formula 180-interior angle. See Exterior Angles of a Polygon
Area	6.182s² approx	Where S is the length of a side. To find the exact area of a decagon or any polygon, using various methods, see Area of a Regular Polygon and Area of an Irregular Polygon

Properties of all nonagons

Number of diagonals	27	The number of distinct diagonals possible from all vertices. (In general ½n(n–3) ). In the figure above, click on "show diagonals" to see them. See Diagonals of a Polygon
Number of triangles	7	The number of triangles created by drawing the diagonals from a given vertex. (In general n–2). In the figure above, click on "show triangles" to see them. See Triangles of a Polygon
Sum of interior angles	1260°	In general 180(n–2) degrees . See Interior Angles of a Polygon

Properties of regular nonagons

Properties of all nonagons

Related polygon topics

General

Types of polygon

Area of various polygon types

Perimeter of various polygon types

Angles associated with polygons

Named polygons