Books Books
After remarking that the mathematician positively knows that the sum of the three angles of a triangle is equal to two right angles...
Yale University Entrance Examinations in Mathematics: 1884 to 1898 - Page 125
1898 - 208 pages

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...

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...

The National Teacher: A Monthly Educational Journal, Volume 4

Education - 1874 - 520 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...

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...

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...

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 is greater...

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...

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...