
Nonagon (9gon) (also Enneagon)
From Latin: nonus  "ninth"
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
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 
Other polygon topics
General
Types of polygon
Area of various polygon types
Perimeter of various polygon types
Angles associated with polygons
Named polygons
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