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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.
Elements of Geometry and Conic Sections - Page 10
by Elias Loomis - 1857 - 226 pages

The Elements of Euclid: The Errors, by which Theon, Or Others, Have Long Ago ...

Robert Simson - Geometry - 1838 - 434 pages
...equal (8. 1.) to the angle CHG; and they are adjacent angles ; but when a straight line standing on a straight line makes 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 to it ;...

Euclid's Elements [book 1-6] with corrections, by J.R. Young

Euclides - 1838 - 264 pages
...EB; therefore the angle AFE is equal* *si to the angle BFE: but when a straight line standing upon another straight line makes the adjacent angles equal to one another, each *s Def.i. of u,,,,,, is a right« angle. there_ fore each of the angles AFE, BFE, is a right angle:...

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

Euclides - 1841 - 378 pages
...expressed by a le:ter placed at that point; as the ' angle at E." X. 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...

Elements of geometry: consisting of the first four,and the sixth, books of ...

Euclides - 1842 - 320 pages
...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 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 - 1842 - 332 pages
...expressed by a letter placed at that point ; as the 'angle at E.' 7. 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...

A course of practical geometry for mechanics

William Pease - Geometry - 1843 - 80 pages
...surface of a sphere, by the intersection of two of its great circles. X. 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...

A system of practical mathematics; being no.xvi. of a new series of school-books

Scottish school-book assoc - 1845 - 434 pages
...at E, it may be called simply the »ngle at E, PLANE GEOMETRY. 9. 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 strnight line which stands on the other is called a perpendicular...

Euclid's Elements of geometry [book 1-6, 11,12] with explanatory notes ...

Euclides - 1845 - 544 pages
...: therefore the angle ADG is equal to the angle GDB: (i. 8.) 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; (i. def. 10.) therefore the angle GDB is a right angle : but FDB is likewise...