- All other four-sided figures besides these are called trapeziums.
[Note. The terms oblong and rhomboid are not often used. Practically the following definitions are used. Any four-sided figure is called a quadrilateral. A line joining two opposite angles of a quadrilateral is called a diagonal. A quadrilateral which has its opposite sides parallel is called a parallelogram'. The words square and rhombus are used in the sense defined by Euclid; and the word rectangle is used instead of the word oblong.
Some writers propose to restrict the word trapezium to a quadrilateral which has two of its sides parallel; and it would certainly be convenient if this restriction were universally adopted.]
Let it be granted,
- That a straight line may be drawn from any one point to any other point:
- That a terminated straight line may be produced to any length in a straight line:
- And that a circle may be described from any centre, at any distance from that centre.