 | George Albert Wentworth - Geometry - 1888 - 264 pages
...third side, and their difference is less than the third side. PROPOSITION XXIII. THEOREM. -/ 138. The sum of the three angles of a triangle is equal to two right angles. A Let ABC be a triangle. To prove Z B + Z BCA + ZA = 2 rt. A. Proof. Suppose CE drawn II to... | |
 | George Johnston Allman - Geometry - 1889 - 266 pages
...drawn from the preceding notices. First inference. — Thales must have known the theorem that the sum of the three angles of a triangle is equal to two right angles. Pamphila, in (d), refers to the discovery of the property of a circle that all triangles described... | |
 | Seth Thayer Stewart - Geometry, Modern - 1891 - 422 pages
...triangle, formed by extending the sides in the same order, is equal to six right angles. PROP. XVII. The sum of the three angles of a triangle is equal to two right angles. PROP. XVIII. The sum of any two angles of a triangle is equal to the supplement of the third... | |
 | George Irving Hopkins - 1891 - 210 pages
...side of a triangle is less than the sum of the other two, and greater than their difference. 98. The sum of the three angles of a triangle is equal to two right angles. Sug. Consult Theorems 58 and 87. 99. If one side of a triangle be extended, the exterior angle... | |
 | Jean-Jacques Rousseau - Education - 1892 - 424 pages
...of mathematieal demonstration. No experimental process can ever establish the general truth that the sum of the three angles of a triangle is equal to two right angles. We should not confound " geometrical recreations " with geometrical science. — (P.) f Isoperimetric... | |
 | William Ezra Worthen - Architectural drawing - 1892 - 850 pages
...equal to the three angles of the triangle, and their sum is equal to two right angles. Therefore, the sum of the three angles of a triangle is equal to two right angles. On one side of a triangle (Fig. 50) construct a triangle equal to the first, with opposite... | |
 | Jean-Jacques Rousseau - Education - 1892 - 424 pages
...of mathematical demonstration. No experimental process can ever establish the general truth that the sum of the three angles of a triangle is equal to two right angle?. We should not confound " geometrical recreations " with geometrical science.—(P.) f Isoperimetric... | |
 | William C. Bartol - Geometry, Solid - 1893 - 106 pages
...lines cannot meet. 353. Any side of a triangle is less than the sum of the other two sides. 354. The sum of the three angles of a triangle is equal to two right angles. 355. Two triangles are equal in all respects when two sides and the included angle of the one... | |
 | John Tilden Prince - Arithmetic - 1894 - 254 pages
...point is equal to 360°. 6. The opposite angles made by two lines crossing each other are equal. 7. The sum of the three angles of a triangle is equal to two right angles. The sum of the angles of a polygon is equal to two right angles taken as many times as the... | |
 | Edwin Pliny Seaver, George Augustus Walton - Arithmetic - 1895 - 412 pages
...it out. Tear off C FIG. 24. two of the angles and place them, as in Fig. 24, so as to show that The sum of the three angles of a triangle is equal to two right angles. e. How many degrees are there in each angle of an equilateral triangle ? /. If the two acute... | |
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After remarking that the mathematician positively knows that the sum of the three angles of a triangle is equal to two right angles... 
