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" Thus when it is said that the sum of the three angles of any triangle is equal to two right angles, this is a theorem, the truth of which is demonstrated by Geometry. "
Elements of Mechanical Drawing - Page 22
by Gardner Chace Anthony - 1894 - 98 pages
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Higher grades

Samuel Hamilton - Arithmetic - 1920 - 362 pages
...with a protractor and find their sum. Repeat this process with other triangles. The sum of all the angles of any triangle is equal to two right angles, or 180°. Written Work The following numbers in each case represent the size of two angles of a triangle. Find...
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Vocational Arithmetic

Clarence E. Paddock, Edward Ellsworth Holton - Arithmetic - 1920 - 250 pages
...obtuse angle, as the triangle MNP. (Fig. 31.) FIG. 30.—Acute Triangle. F 7 G. 31.—Obtuse Triangle. The sum of the three angles of any triangle is equal to 180 degrees or two right angles. The sum of the two acute angles of a right triangle is equal to 90...
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A History of Greek Mathematics, Volume 1

Sir Thomas Little Heath - Mathematics - 1921 - 482 pages
...parallel lines, which they used for the purpose of establishing by a general proof the proposition that the sum of the three angles of any triangle is equal to two right angles. This latter proposition they again used to establish the well-known theorems about the sums of the...
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Questions Set at the Examinations, Volume 1922

College Entrance Examination Board - Universities and colleges - 1922 - 124 pages
...credits will not be given on this paper for plane geometry and solid geometry. Take ir=3} 1. Prove: The sum of the three angles of any triangle is equal to two right angles. 2. Prove: If two triangles have their sides respectively proportional, the triangles are similar. 3....
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Plane Geometry

Walter Burton Ford, Charles Ammermann - Geometry, Modern - 1923 - 406 pages
...CD. [HiNT. Show that the A ACD and ABE are congruent.] PART III. ANGLES AND TRIANGLES 62. Theorem XI. The sum of the three angles of any triangle is equal to two right angles, or 180P. Given any triangle A BC. To prove that Z^ + ZB + ZC = 2rt. A. Proof. Prolong AB to D and through...
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Plane and Solid Geometry

Walter Burton Ford, Charles Ammerman - Geometry, Plane - 1923 - 414 pages
...and E lie on opposite sides of AB. Prove that BE=CD. PART III. ANGLES AND TRIANGLES 62. Theorem XI. The sum of the three angles of any triangle is equal to two right angles, or 180°. Given any triangle ABC. To prove that Z/l + ZB + ZC=2rt. A Proof. Prolong AB to D and through B draw...
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Elementary Mechanical Drawing: Theory and Practice, with Chapters on ...

Charles William Weick - Geometrical drawing - 1925 - 276 pages
...between 90° and 180°. TRIANGLES 320. A triangle is any plane figure bounded by three straight lines. The sum of the three angles of any triangle is equal to 180°. If one of the angles is 90°, or a right angle, the sum of the other two is 90°. In radian...
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The New Mathematics, Book 2

John Charles Stone - Mathematics - 1926 - 344 pages
...by all three angles of the triangle? By trying this experiment with any triangle, you will find that The sum of the three angles of any triangle is equal to 180 degrees. 12. How many degrees in each angle of an equilateral triangle ? (The angles are all equal.)...
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Biennial Report of the State Superintendent of Public Instruction ..., Volume 12

Education - 1893 - 650 pages
...Write two postulates and two axioms. 3. Define chord, segment, sector, polygon. 4. Demonstrate that the sum of the three angles of any triangle is equal to two right angles. 5. Demonstrate that any angle formed by a tangent and a chord is measured by one-half the intercepted...
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The Pythagorean Sourcebook and Library: An Anthology of Ancient Writings ...

Kenneth Sylvan Guthrie, David R. Fideler - Philosophy - 1987 - 374 pages
...parallel lines, which they used for the purpose of establishing by a general proof the proposition that the sum of the three angles of any triangle is equal to two right angles. This latter proposition they again used to establish the well-known theorems about the sums of the...
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