Page:The Elements of Euclid for the Use of Schools and Colleges - 1872.djvu/27

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DEFINITIONS.
  1. A term or boundary is the extremity of any thing.
  2. A figure is that which is enclosed by one or more boundaries.
  3. float
    A circle is a plane figure contained by one line, which is called the circumference, and is such, that all straight lines drawn from a certain point within the figure to the circumference are equal to one another:
  4. And this point is called the centre of the circle.
  5. A diameter of a circle is a straight line drawn through the centre, and terminated both ways by the circumference.

    [A radius of a circle is a straight line drawn from the centre to the circumference.]

  6. A semicircle is the figure contained by a diameter and the part of the circumference cut off by the diameter.
  7. A segment of a circle is the figure contained by a straight line and the circumference which it cuts off.
  8. Rectilineal figures are those which are contained by straight lines:
  9. Trilateral figures, or triangles, by three straight lines:
  10. Quadrilateral figures by four straight lines:
  11. Multilateral figures, or polygons, by more than four straight lines.
  12. float
    Of three-sided figures,

    An equilateral triangle is that which has three equal sides:


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