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

## Plane and Solid Geometry

William James Milne - Geometry - 1899 - 398 pages
...49°, and 74° ? PLANE GEOMETRY.— BOOK I. Ex. 59. Show by each of the following figures that the sum of the three angles of a triangle is equal to two right angles, assuming that the construction lines are drawn as they appear to be drawn. Proposition XXIII...

## Plane Geometry

George Albert Wentworth - Geometry, Plane - 1899 - 278 pages
...sides opposite the equal angles are called homologous sides. PROPOSITION XVIII. THEOREM. 129. Tfie sum of the three angles of a triangle is equal to two right angles. Let A, B, and BCA be the angles of the triangle ABC. To prove that ZA + ZB + Z BCA = 2 rt....

## A Textbook on Sheet-metal Pattern Drafting, Volume 1

Metal-work - 1901 - 548 pages
...pentagon are 40.5, 30.6'>, 51.25, 32.75, and 36.85; find the perimeter. Ans. 192 ft. TRIANGLES. 47. The sum of the three angles of a triangle is equal to two right angles, <>r 180°. Thus, the sum of the three angles A, B, and C, Fig. 31, is 59° + 73° + 48° =...

## Elementary Geometry, Plane and Solid: For Use in High Schools and Academies

Thomas Franklin Holgate - Geometry - 1901 - 462 pages
...equals the sum of Zs CAB and CBA That is, Z.ACD equals the sum of Zs CAB and CBA. 101. COROLLARY I. The sum of the three angles of a triangle is equal to two right angles. 102. COROLLARY II. The two acute angles of any right triangle are complementary ; ie their...

## International Education Series

William T. Harris, A. M., LL. D. - 1902 - 420 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 angles. We should not confound " geometrical recreations'" with geometrical science.—(P.) t Isoperimetric...

## The School World: A Monthly Magazine of Educational Work and Progress, Volume 5

Education - 1903 - 692 pages
...uniformly. Casey (El. of Euclid, 8th ed., p. 299) says : " The discovery of the proposition that ' the sum of the three angles of a triangle is equal to two right angles ' is attributed to Pythagoras. Until modern times no proof of it, independent of the theory...

## Biennial Report of the Superintendent of Public Instruction ..., Volumes 17-19

Education - 1904 - 938 pages
...straight line joining their centers is the perpendicular bisector of their common chord. 6. Prove: The sum of the three angles of a triangle is equal to two right angles. 7. (a) Circumscribe a circle about a given triangle. (&) Inscribe a circle In a given triangle....

## The Presbyterian Quarterly, Volume 5

Presbyterianism - 1891 - 656 pages
...tests of other rational processes. This is true in mathematics. Thus, when once it is proven that the sum of the three angles of a triangle is equal to two right angles, no rational process can be accepted as true which in premise or conclusion contravenes this...