| George Albert Wentworth - Geometry - 1877 - 416 pages
...point to a straight line make equal acute angles with that line. PROPOSITION XXI. THEOREM. 98. The sum of the three angles of a triangle is equal to two righd angles. BE C Let ABC be a triangle. We are to prove Z. B + Z. BCA + Z. A = two rt. A. Draw CE... | |
| Education - 1907 - 700 pages
...scientific accuracy is proverbial. It is susceptible of definite proof that two and two make four; that the, sum of the three angles of a triangle is equal to two right angles and nothing else. There need never be any question as to what will result when carbon burns... | |
| James Bates Thomson - Algebra - 1880 - 324 pages
...on. Hence, the proposition must be universally true. 466. In Geometry, we have the proposition : TJie sum of the three angles of a triangle is equal to two right angles. We find it to be true in one case ; then in another, etc. Hence, we conclude the proposition... | |
| Alexis Claude Clairaut - 1881 - 184 pages
...opposite sides of a straight line which cuts two parallels ........ 36 These angles are equal 37 64. The sum of the three angles of a triangle is equal to two right angles 37 68. The exterior angle of a triangle is equal to the sum of its two interior opposite angles... | |
| Daniel Seely Gregory - Logic - 1881 - 236 pages
...best policy. 15. Education cannot be effected by mere class-room instruction or lecturing. 16. The sum of the three angles of a triangle is equal to two right angles. 17. Two straight lines cannot inclose a space. 18. The earth is between 93,000,000 and 94,000,000... | |
| George Albert Wentworth - 1881 - 266 pages
...perpendicular, each to each, they are either equal or supplementary. PROPOSITION XXI. THEOREM. 98. The sum of the three angles of a triangle is equal to two right angles. BE С Let AB С be a triangle. We are to prove ¿ B + ZB С A + ¿ A = two rt. A. Draw С E... | |
| Electronic journals - 1882 - 432 pages
...of those numbers, say Sj, ¿2, . . . ^. These divisors necessarily * Take as an example the theorem that the sum of the three angles of a triangle is equal to rightangles : as soon as by a stroke of the imagination a line is conceived as drawn from one angle... | |
| George Albert Wentworth - Geometry, Modern - 1882 - 268 pages
...perpendicular, each to each, they are either equal or supplementary. PROPOSITION XXI. THEOREM. 98. The sum of the three angles of a triangle is equal to two rig/'t angles. С Let ABC be a triangle. We are to prove Z. B + ZB С A + ZA = two rt. A. Draw С E... | |
| Charles Sanders Peirce, Allan Marquand - Logic, Symbolic and mathematical - 1883 - 228 pages
...correct analysis of the nature of probability. After remarking that the mathematician positively knows that the sum of the three angles of a triangle is equal to two right angles because he apprehends the geometrical proof, he then continues : " But another man who never... | |
| Philosophy - 1884 - 462 pages
...negation ; and, of course, what is true of triangle is true of all general ideas ; they are negations. The sum of the three angles of a triangle is equal to two right angles. This is a proposition to be demonstrated. I draw a triangle, and prove that the three angles... | |
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