Page 217 - Start Up Mathematics_8 (Non CCE)

Classification of Polygons
Table 14.1
No. of sides Sum of interior No. of sides Classification Sum of interior

or vertices Classification angles or vertices angles
Triangle Octagon
I
3 180º II 1,080º
I 8 III IV (6 × 180º)
V
Quadrilateral VI

360º Nonagon
4 I (2 × 180º) I II
II 9 III IV 1,260º

V VI (7 × 180º)
Pentagon
VII
I 540º
5 Decagon
II (3 × 180º)
III I
II III 1,440º
Hexagon 10 IV V (8 × 180º)
6 II 720º VI
I IV (4 × 180º) VII
III VIII
Heptagon n n-gon (n – 2) × 180º

I 900º
7
II (5 × 180º)
III diagonals
IV V
D 2
D 1
Diagonals
The line segments obtained by joining non-adjacent vertices are called diagonals of the polygon.
D and D are the two diagonals in Fig. 14.8. Fig. 14.8
2
1
Regular and Irregular Polygons
In a regular polygon (Fig. 14.9), all sides are of the same
length (equilateral) and all angles are of the same measure
(equiangular).
(a) (b)
Fig. 14.9

A polygon which is not regular is an irregular
polygon (Fig. 14.10).

(a) (b)
Fig. 14.10

209