29. An obtuse-angled triangle has ene obtuse angle.

30. An acute-angled triangle has all its three angles acute.

31. A figure of four sides and angles is called a quadrangle, or a quadrilateral.

32. A parallelogram is a quadrilateral, which has both pair of its opposite sides parallel. And it takes the following particular names.

33. A rectangle is a parallelogram, having all its angles right.

34. A square is an equilateral rectangle, having all its sides equal, and all its angles right.

35. A rhomboid is an oblique-angled parallelogram.

36. A rhombus is an equilateral rhomboid, having all its sides equal, but its angles oblique.

A 42

37. A.

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 nonagon, 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 being also called a trigon, and the latter a tetragon.

Pentagon.

Hexagon.

Heptagon.

45. The radius of a circle is a right line, drawn from the centre to the circumference.

46. The diameter of a circle is a right line, drawn through the centre, and terminating in the circumference on both sides.

47. An arc of a circle is any part of the circumference.

48. A chord is a right line, joining the extremities of an arc.

49. A segment is any part of a circle, bounded by an arc and its chord.

50. A semicircle is half the circle, or a segment cut off by a di

ameter.

51. A sector is any part of a circle, bounded by an arc, and two radii, drawn to its extremities.

52. A quadrant, or quarter of a circle, is a sector, having a quarter of the circumference for its arc, and its two radii are perpendicular to each other.

53. The height, or altitude, of a figure is a perpendicular let fall from an angle, or its vertex, to the opposite side, called the base.

54. In a right-angled triangle, the side opposite to the right angle is called the hypotenuse; and the other, two the legs, or sides, or sometimes the base and perpendicular.