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" ... the three angles of a triangle are together equal to two right angles, although it is not known to all. "
An essay on mechanical geometry, explanatory of a set of models - Page 14
by Benjamin Donne - 1796
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The Popular Educator, Volumes 1-2; Volume 12

Geography - 1867 - 960 pages
...OüTUSE-ütOLSD, Having one obtuse angle, and, of necessity, twoacuteangles. Now, as the three interior angles of a triangle are together equal to two right angles or 180 degrees, and as an obtuse angle is any angle greater than a right angle or 90 degrees, while an...
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Elements of Trigonometry, Plane and Spherical: With the Principles of ...

John Wright (Mathematician) - Perspective - 1772 - 302 pages
...ninety degrees. The ambiguity is avoided, if the fum of the other two angles be known ; becaufe [32. IJ the three angles of a triangle are together equal to two right angles. PROP. V. THEOR. Fig. 14. 5. The fum of any fwofides, BA.and AC, of any triangle ABC, is to the difference...
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Letters of Euler to a German Princess, on Different Subjects in ..., Volume 2

Leonhard Euler - Science - 1802 - 696 pages
...impoffible to draw any concluiion, with refpect to real objects : thus, when I have demonftrated that the three angles of a triangle are together equal to two right angles, this is a property belonging only to an abilract triangle, and not at all to one really exifting. But...
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The Edinburgh Review, Volume 15

English literature - 1810 - 556 pages
...ever been deduced. If we could demonftrate, independently of all confideration of parallel lines, that the three angles of a triangle are together equal to two right angles, the object in view would be accomplifhed, and the difficulty, in this part of the Elements, would be...
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Easy Introduction to Mathematics, Volume 2

Charles Butler - 1814 - 568 pages
...draw DF parallel to CE, and ECDF will be the rectangle contained by A and B, as was required ". « The three angles of a triangle are together equal to two right angles (Enclid 38. 1.) that is, to 180°; wherefore if the sum of two angles of a triangle be subtracted from...
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Works, with a memoir of the author, Volume 4

John Playfait - 1822
...ever been deduced. If we could demonstrate, independently of all consideration of parallel lines, that the three angles of a triangle are together equal to two right angles, the object in view would be accomplished, and the difficulty, in this pait of the Elements, would be...
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The Works of John Playfair ...: With a Memoir of the Author ...

John Playfair - Science - 1822 - 552 pages
...ever been deduced. If we could demonstrate, independently of all consideration of parallel lines, that the three angles of a triangle are together equal to two right angles, the object in view would be accomplished, arid the difficulty, in this part of the Elements, would...
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The Boston Journal of Philosophy and the Arts, Volume 3

Science - 1826 - 628 pages
...line, are true for the perpendicular. The Problem for drawing parallel lines may follow here. Theorem. The three angles of a triangle are together equal to two right angles. For a demonstration, see any treatise on geometry. Theorem. Lacroix, No. 54. The parts AC and BD, (fig....
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Geometry, Plane, Solid, and Spherical, in Six Books: To which is Added, in ...

Pierce Morton - Geometry - 1830 - 584 pages
...notwithstanding, of opinion, that the grand truth with which it is so intimately connected, viz., that " the three angles of a triangle are together equal to two right angles," may be referred to the general principle of liomogeneity. Of this it is unnecessary to suy more in...
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The Mechanics' Magazine, Museum, Register, Journal, and Gazette, Volume 15

Industrial arts - 1831 - 532 pages
...It has been before proved that the angle ADe is an acute angle of 90 degrees, whence it follows that as the three angles of a triangle are together equal to two right angles, the remaining angle fh D must likewise be an acute angle of 90 degrees, and, as before, since the two...
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