G1a – 2D geometry – terms and notation

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Prerequisites
None.

 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.

Links to past exam questions

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In the real world

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