Decagon

A decagon is a polygon with ten sides and ten interior angles. Its sides may be equal or unequal, and its angles need not be regular.

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Polygon: A closed plane figure formed by a finite sequence of straight line segments. A decagon is the ten-sided member of this broader family.
Interior angle sum: The total measure of a polygon’s interior angles, equal to (n−2) × 180° for an n-sided polygon. For ten sides, this gives a decagon’s total interior angle measure of 1,440°.
Decagram: A ten-pointed star polygon formed by connecting selected vertices of a regular decagon. It is a star-shaped figure built from the vertices of a regular decagon.
Nonagon: A polygon with nine sides and nine angles. One fewer side changes the angle sum and eliminates decagonal symmetry patterns.
Interior angle: An angle formed inside a polygon by two adjacent sides. The ten interior angles determine a decagon’s total angle sum.
Regular decagon: A decagon with ten equal sides and ten equal interior angles. Its symmetry makes angle, perimeter, and area calculations especially direct.
Decagonal tiling: A tiling pattern that uses decagonal shapes as repeating or recurring tiles. Decagons can fill patterns when combined with other polygons or used in nonperiodic arrangements.
Hendecagon: A polygon with eleven sides and eleven angles. One additional side distinguishes this neighboring polygon from a decagon.
Exterior angle: An angle formed between one side of a polygon and an extension of an adjacent side. Exterior turns reveal how a decagon’s boundary changes direction.
Perimeter: The total length of a closed figure’s boundary. A decagon’s perimeter is the sum of its ten side lengths.