3^^ GEOMETRY, 



37. A trapezium is a quadrilateral, which 

 has not both pair of its opposite sides 

 parallel. 



38. A trapezoid has only one pair of 

 Opposite sides parallel. 



39. A diagonal is a right line, joining 

 any two opposite angles of a quadrilateral. 



40. Plane figures, having more than four sides, are, in 

 general, called polygons ; and they receive other particular 

 names, according to the number of their sides or angles. 



41. A pentagon is a polygon of five sides ; a hexagon 

 has six sides ; a heptagon, seven ; an octagon, eight ; a non- 

 agon, nine ; a decagon, ten ; an undecagon, eleven ; and a 

 dodecagon, twelve. 



42. A regular polygon has all its sides and all its angles 

 equal. — If they be not both equal, the polygon is ir- 

 regular. 



43. An equilateral triangle is also a regular figure of 

 three sides, and the square is one of four ; the former be- 

 ing also called a trigon, and the latter a tetragon. 



Pentagon. Hexagon. 



