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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: Containing the First Six Books of Euclid, with a ... - Page 9
by John Playfair - 1860 - 317 pages

Euclid's Elements of Geometry: From the Latin Translation of Commandine. To ...

John Keill - Logarithms - 1723 - 444 pages
...the Angle AFE j. g ti fhall bef equal to the Angle BFE. But when a Right Line {landing upon a Right Line makes the adjacent Angles equal to one another, each of the equal Angles is ia Right Angle. Wherefore AFE, or BFE, is a Right Angle. And therefore the Right Line...

Euclid's Elements of Geometry,: From the Latin Translation of Commandine. To ...

Euclid, John Keill - Geometry - 1733 - 444 pages
...Therefore the Angle * 8- i. AD G is * equal to the Angle GD B. But when a Right Line ftanding upon 'a Right Line, makes the adjacent Angles equal to one another, each of the 10. i. equal Angles will f be a Right Angle. Wherefore the Angle GDB is a Right Angle. But FDB is alfo...

The Young Mathematician's Guide: Being a Plain and Easy Introduction to the ...

John Ward - Mathematics - 1747 - 492 pages
...is, AC, and C J5, are Perpendicular to £> C, as well as -D, C is to /•j'r/W or both of them. g. An OBTUSE ANGLE is that which is greater than a Right Angle. Such is the Angle included between the Lines AC and n CB. 10. An ACUTE ANGLE is that ^_ which is lefs...

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

Robert Simson - Trigonometry - 1762 - 488 pages
...the angle ADG is equal c to the angle GDB. but when a ftraight line ftanding upon another ftraight line, makes the adjacent angles equal to one another ,each of the angles is a right angle *. therefore the angle GDB is a right angle. but FDB is like- d.io.Def.i. wife a right...

Euclid's Elements of Geometry: The First Six, the Eleventh and Twelfth Books

Euclid - Geometry - 1765 - 492 pages
...angle EH c [by prop. 8.] ; and thefe are adjacent angles. But when a right line flanding upon a right line makes the adjacent angles equal to one another, each of the equal angles is a right angle, and the ftanding right line is called a perpendicular to that upon which...

Instructions Given in the Drawing School Established by the Dublin Society ...

Joseph Fenn - Mathematics - 1769 - 536 pages
...When a ftraight line (AB) {landing on another ftright line (CD) makes the adjacent angles (ABD, ABC,) equal to one another, each of the angles is called a right angle ; and the rtraight line (AB) which ftands on the other (CD) is called я perpendicular. Fig. 7. XI. An Obtvfe...

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

Robert Simson - Trigonometry - 1775 - 534 pages
...is equal c to the angle GDB: But when a ftraight line ftanding upon another ftraight line makes .A. the adjacent angles equal to one another, each of the angles is a right angle d : Therefore the angle GDB is a " d to. def. i« right angle : But FDB is likewife a...

The Elements of Euclid: With Dissertations Intended to Assist and Encourage ...

Euclid, James Williamson - Euclid's Elements - 1781 - 324 pages
...8. i.) the angle AFE is equal to the angle BFE : but when a ftraight line ftanding upon a ftraight line makes the adjacent angles equal to one another, each of the equal angles is a right angle ; therefore each of the angles AFE, BFE is a right angle : therefore...