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Names of 2D polygons based on number of sides (or edges)
Where the polygon has more than one name, the most common one is given first:
- 3 sides: triangle
- 4 sides: quadrilateral
- 5 sides: pentagon
- 6 sides: hexagon
- 7 sides: heptagon or septagon
- 8 sides: octagon
- 9 sides: nonagon or enneagon
- 10 sides: decagon
- 11 sides: hendecagon or undecagon
- 12 sides: dodecagon
- 13 sides: triskaidecagon
See G4a – Properties of special triangles and quadrilaterals for more on particular types of triangles and quadrilaterals.
2D geometry – terms and notation
This lesson covers the following key words: edge, vertex, equal edges and angles, and parallel.
The definitions of acute, right, obtuse and reflex angles are covered in lesson G15a.
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