After remarking that the mathematician positively knows that the sum of the three angles of a triangle is equal to two right angles... Introduction and books 1,2 - Page 218by Euclid, Sir Thomas Little Heath, Johan Ludvig Heiberg - 1908Full view - About this book
| George Albert Wentworth - Geometry - 1877 - 402 pages
...a point to a straight line make equal acute angles with that line. PROPOSITION XXL THEOREM. 98. The **sum of the three angles of a triangle is equal to two right** angles. BE C Let ABC be a triangle. We are to prove ZB + ZB CA + ZA = two rt. A Draw CE II to AB, and... | |
| George Albert Wentworth - Geometry - 1877 - 398 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
...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 - 312 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... | |
| George Albert Wentworth - Geometry, Plane - 1881 - 250 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... | |
| Daniel Seely Gregory - Logic - 1881 - 210 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... | |
| Alexis Claude Clairaut - 1881
...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... | |
| George Albert Wentworth - Geometry, Plane - 1882 - 250 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... | |
| Studies - 1883 - 203 pages
...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... | |
| William Torrey Harris - Philosophy - 1884
...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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