Triangle. The sum of two sides of a triangle (Fig. 79) is always greater than the third side: b + c > a. The sum of angles of a triangle: α + β + γ = 180°. A triangle is completely determined, when there are given: (1) three sides or (2) two sides and the angle included between them, or (3) one side and two angles adjacent to it. Two sides and an angle opposite to one of them determine either two triangles or one, or no triangle, in various cases (see Fig. 80, and, for details, pp. 221, 222).
KeywordsDihedral Angle Regular Polygon Plane Angle Central Angle Interior Angle
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© Verlag Harri Deutsch, Zürich 1973