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An exterior angle of a triangle is equal to the sum of the two opposite interior angles.
Junior High School Mathematics ... - Page 25
by Edson Homer Taylor, Fiske Allen - 1923

An Introduction to Geometry and the Science of Form: Prepared from the Most ...

Anna Cabot Lowell - Geometry - 1846 - 161 pages
...other. 134. The exterior angle of a triangle, that is, the angve made by producing one of the sides of a triangle, is equal to the sum of the two opposite interior angles, (fig. 88.) Angle ACD = angle ABC + angle CAB. Dem. ACD + ACB = 2 RA; ABC + CAB -f ACB = 2 RA; therefore...

Elemento of Geometry, Theoretical and Practical: Containing a Full ...

George Clinton Whitlock - Mathematics - 1848 - 324 pages
...Triangle is equal to a right angle Cor. 8. The external angle formed by producing one of (94) the sides of a triangle, is equal to the sum of the two opposite internal angles. Let a, b, c, be the three angles of any triangle, and с adjacent to the external...

Report of the Superintendent of Public Instruction

Michigan. Department of Public Instruction - Education - 1893 - 562 pages
...done in the simplest manner you can conceive. GEOMETRY. Demonstrate the following propositions: 1. Any exterior angle of a triangle is equal to the sum of the two opposite interior angles. 2. If the squares of the sides of a quadrilateral are together equivalent to the squares of the diagonals,...

Graded Course of Instruction for the Public Schools of Chicago

Chicago (Ill.). Board of Education - Elementary schools - 1872 - 115 pages
...right angles. a=db=ec=c d-{-e+c=a + b + c, or a flat angle, or two right angles. THEOREM II.—The exterior angle of a triangle is equal to the sum of the two opposite interior angles. g + d= 2 right angles. c+d+e=^2 right angles. g+d=c+d+c. In the following figures, mark and name angles....

A Treatise on Special, Or Elementary Geometry

Edward Olney - Geometry - 1872 - 472 pages
...formed by any side with its adjacent side produced, as CBD, Fig. 174. PROPOSITION IT* 231. TJteorem. — An exterior angle of a triangle is equal to the sum of the two interior non-adjacent angles. DEM. — Let ABC be any triangle, and CBD an exterior angle;...

A Treatise on Special Or Elementary Geometry, Volumes 1-2

Edward Olney - Geometry - 1872 - 566 pages
...formed by any side with its adjacent side produced, as CBD, Fig. 174. PROPOSITION IT. 231. TJieorem. — An exterior angle of a triangle is equal to the sum of the two interior non-adjacent angles. DEM. — Let ABC be any triangle, and CBD an exterior angle;...

The elements of geometry, in eight books; or, First step in applied logic

L J V. Gerard - 1874
...ABC [II. 21]: therefore the three angles are together equal to two right angles, WWTBD COROLLARY I. An exterior angle of a triangle, is equal to the sum of the two oppositeinterior angles. COROLLARY II. If two angles of a triangle be equal to two angles of...

Elements of Plane and Solid Geometry

George Albert Wentworth - Geometry - 1877 - 442 pages
...one third of two right angles, or two thirds of one right angle. PROPOSITION XXII. THEOREM. 105. The exterior angle of a triangle is equal to the sum of the two opposite interior angles. a Let BC H be an exterior angle of the triangle ABC. We are to prove Z BCH= Z. A + ZB Z. B С 11+ Z...