« ForrigeFortsett »
See Y. straight line between them lies wholly in that superficies.
VIII. " A plane angle is the inclination of two lines to one another in a “ plane, which meet together, but are not in the same direction.”
IX. A plane rectilineal angle is the inclination of two straight lines to one another, which meet together, but are not in the fame straight line.
'N. B. When several angles are at one point B, any one of them is expressed by three letters, of which the letter that is at the vertex
of the angle, that is at the point in which the straight lines that 'contain the angle meet one another, is put between the other two * letters, and one of these two is somewhere upon one of those straight * lines, and the other upon the other line. thus the angle which is
contained by the straight lines AB, CB is named the angle ABC, or CBA; that which is contained by AB, DB is named the angle ABD, or DBA; and that which is contained by DB, CB is called
the angle DBC, or CBD. but if there be only one angle at a point, ‘it may be expressed by a letter placed at that point; as the angle " at E.'
straight line makes the adjacent angles
Book 1. 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 cer. tain point within the figure to the circumference, are equal to one another.
XVII. A diameter of a circle is a straight line drawn thro' the center, atid See Ni terminated both ways by the circumference.
XVIII. A semicircle is the figure contained by a diameter and the part of the circumference cót off by the diameter.
and all its angles right angles.
not right angles.
ther, but all its sides are not equal, nor its angles right angles,
Book 1. All other four fided figures besides these, are called Trapeziums.
being produced ever so far both ways, do not meet.
POSTULAT E S.
from that center,
A X I 0 MS.