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“ in a plane, which meet together, but are not in the fame
lines to one another, which meet together, but are not in
• N. B.
•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 r 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; the angle at E.'
ther straight line makes the adjacent
led the circumference, and is such that all straight lines
equal, and all its angles right angles.
are not right angles.
another, but all its Gdes are not equal, nor its angles rigîio