GEOMETRY. 353 



right angles, the parallelogram is called a rhombus, 

 as Fig. 10. 



21. A parallelogram having all its angles oblique, 

 arid only its opposite equal, is called a rhomboid, 

 as Fig. 9. 



2%. When a quadrilateral or four-^sided figure 

 has none of its sides parallel, it is called a trape- 

 zium, as Fig. 13. ; consequently every quadrangle, 

 or quadrilateral which is not a parallelogram, is a 

 trapezium. 



23. A trapezoid has only one pair of its sides 

 parallel, as Fig. 14. 



24. A diagonal is a right line drawn between 

 any two angles that are opposite in a quadrangle, 

 as I K, Fig. 15. In parallelograms the diagonal is 

 sometimes called the diameter, because it passes 

 through the centre of the figure. 



25. Complements of a parallelogram. If any 

 point, as E (Fig. 15.), be taken in the diagonal of a 

 parallelogram, and through that point two lines are 

 drawn parallel to the sides, as A B, C D, it will be 

 divided into four parallelograms, D D, L, F, G G. 

 The two divisions, L, F, through which the diame- 

 ter does not pass, are called the complements. 



26. Figures having more than four sides are 

 called polygons. If the sides are all equal, they 

 are called regular polygons: if they are unequal, 

 they are called irregular polygons. 



A pentagon is a polygon of five sides. 



A hexagon has six sides. 



A heptagon seven sides. 



An octagon eight sides. 



A nonagon nine sides. 



An un decagon eleven sides. 



A duodecagon twelve sides. 



VOL. II. A A 



