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Classification of Polygons

Polygons are classified according to the number of sides or vertices they have.

• Triangle: (Tri stands for three) A triangle has three sides and three vertices.
• Quadrilateral: (Quad stands for four) A quadrilateral has four sides and four vertices.

• Pentagon: (Penta stands for five) A pentagon has five sides and five vertices.
• Hexagon: (Hexa stands for six) A hexagon has six sides and six vertices.

• Heptagon: (Hepta stands for seven) A heptagon has seven sides and seven vertices.
• Octagon: (Octa stands for eight) An octagon has eight sides and eight vertices.

• Nonagon: (Nona stands for nine) A nonagon has nine sides and nine vertices.
• Decagon: (Deca stands for ten) A decagon has ten sides and ten vertices.

Number of Classification Figure Number of Classification Figure
sides sides

3 Triangle 7 Heptagon

4 Quadrilateral 8 Octagon

5 Pentagon 9 Nonagon

6 Hexagon 10 Decagon

Note: A polygon with n sides is called n-gon.

Diagonals in Polygons
A B
A diagonal is a line segment connecting two non-consecutive vertices of a
polygon. In other words, the line segments obtained by joining vertices that
are not adjacent are called diagonals of a polygon. In the adjoining figure,
AC and BD are diagonals of polygon ABCD. D C

Triangle Quadrilateral Pentagon Hexagon
3 sides, 0 diagonals 4 sides, 2 diagonals 5 sides, 5 diagonals 6 sides, 9 diagonals
(
nn − ) 3
The number of diagonals of a polygon are calculated by using the formula , where n is the
number of sides of the polygon. 2

57 Quadrilaterals