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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... "
Elements of Geometry and Trigonometry: With Applications in Mensuration - Page 60
by Charles Davies - 1886 - 324 pages
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The American Journal of Education, Volume 23

Henry Barnard - Education - 1872 - 988 pages
...catch either into other cogged wheels, or into pinions, or into trundles, Ac. Of the Triangk. — The sum of the three angles of a triangle is equal to two right-angles, Ac. Of similar Triangles. — Two triangles are similar when the angles of one are equal...
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A Manual of Discipline and Instruction for the Use of the Teachers of the ...

New York Board of Education, New York (N.Y.). Board of Education - History - 1873 - 166 pages
...side in -each respectively equal ; (c) when they have three sides in each respectively equal. 6. The sum of the three angles of a triangle is equal to two right angles. I7. The sum of the interior angles of a polygon is equal to twice as many right angles as the...
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The National Teacher: A Monthly Educational Journal, Volume 4

Education - 1874 - 526 pages
...heartfelt pleasure and profound satisfaction from the contemplation of that wonderful truth, that the sum of the three angles of a triangle is equal to two right angles. My friend, who sits before me, used to take particular delight in putting this at me, when...
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The Ohio Educational Monthly: A Journal of School and Home Education, Volume 23

Education - 1874 - 508 pages
...heartfelt pleasure and profound satisfaction from the contemplation of that wonderful truth, that the sum of the three angles of a triangle is equal to two right angles. My friend, who sits before me, used to take particular delight in putting this at me, when...
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How to Teach: A Manual of Methods for a Graded Course of Instruction... for ...

Henry Kiddle, Thomas F. Harrison, Norman Allison Calkins - Teaching - 1875 - 294 pages
...equality as a definite fact, and inequality indefinitely. Thus, it is required to be proved that the sum of the three angles of a triangle is equal to two right angles ; also, that, of any two sides of a triangle, that which lies opposite to the greater angle...
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Elements of Geometry with Exercises for Students: An an Introduction to ...

Aaron Schuyler - Geometry - 1876 - 384 pages
...equal. 76. Exercises. 1. Prove by means of the annexed diagram, in which DE is parallel to AC, that the sum of the three angles of a triangle is equal to two right angles. 2. The sum of the three straight lines drawn from any point within a triangle to the vertices...
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Hermathena, Volume 3

Humanities - 1877 - 626 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 [<f], refers to the discovery of the property of a circle that all triangles described...
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Elements of Plane and Solid Geometry

George Albert Wentworth - Geometry - 1877 - 416 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...
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Elements of Plane and Solid Geometry

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...
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New Practical Algebra: Adapted to the Improved Methods of Instruction in ...

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...
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