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When a straight line standing on another straight line makes the adjacent angles equal to one another, each of the angles is called a right angle ; and the straight line which stands on the other is called a perpendicular to it.
The Elements of geometry; or, The first six books, with the eleventh and ... - Page 2
by Euclides - 1855

The Elements of Euclid; viz. the first six books, together with the eleventh ...

Euclides - 1834 - 518 pages
...the base CG: therefore the angle CHF is equal* to the angle CHG ; and they are adjacent angles: but when a straight line, standing on another straight...the adjacent angles equal to one another, each of them is a right angle, and the straight line. which stands upon the other, is called a perpendicular...

The Elements of Euclid: Viz. the First Six Books, Together with the Eleventh ...

Euclid - 1835 - 540 pages
...contained by BD, 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.' X. When a straight line standing on another straight line makes the adja- • cent angles equal to...

Library of Useful Knowledge: Geometry, plane, solid, and spherical [by ...

Mathematics - 1835
...letter, as A, always denotes the angular point. 10. (Eue. i. det 10.) When a straight line standing; upon another straight line makes the adjacent angles equal to one another, each of them is called a right angle, and the straight line which stands upon the other is called a perpendicular...

The Teacher's Assistant in the "Course of Mathematics Adapted to the Method ...

Mathematics - 1836 - 472 pages
...of two straight lines to one another, which meet together but are not in the same straight line. 7. When a straight line standing on another straight...the adjacent angles equal to one another, each of the angles is called a right angle ; and the straight line which stands on the other is called a perpendicular...

Elements of Geometry: Containing the First Six Books of Euclid, with a ...

John Playfair - Euclid's Elements - 1836 - 488 pages
...angle at a point, it may be expressed by a letter placed ' at that point ; as the angle at E.' VII. When a straight line standing on another straight line makes the adjacent angles equal to one an, other, each of the angles is called a right angle; and the straight line which stands on the other...

The Element of Geometry

John Playfair - Geometry - 1836 - 114 pages
...therefore the angle ADG is equal (7. 1.) to the angle BDG ; but when a straight line standing upon another straight line, makes the adjacent angles equal to one another, each of the angles is a right angle (Def. 27. 1.); therefore BDG is a right angle ; but BDF is likewise a right...

The First Six and the Eleventh and Twelfth Books of Euclid's Elements: With ...

Euclid - Geometry - 1837 - 410 pages
...meet one another.^ The point in which the straight lines meet is called the vertex of the angle. 8. When a straight line standing on another straight...the adjacent angles equal to one another, each of the angles is called a right angle; and the straight line which stands on the other is called a perpendicular...

Elements of Plane Geometry According to Euclid

Andrew Bell - Euclid's Elements - 1837 - 240 pages
...contained by BD, CB, is called the angle DBG, 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. It is sometimes convenient to name an angle by a small letter placed within the angle ; thus, angle...