TAILIEUCHUNG - Handbook of mathematics for engineers and scienteists part 12

Table permits one to find the sides and angles of an arbitrary triangle if three appropriately chosen sides and/or angles are given. From the relations given in Tables and . one can derive all missing relations by cyclic permutations of the sides a, b, and c and the angles a. 3, and " | . Plane Geometry 45 Table permits one to find the sides and angles of an arbitrary triangle if three appropriately chosen sides and or angles are given. From the relations given in Tables and one can derive all missing relations by cyclic permutations of the sides a b and c and the angles a 3 and 7. TABLE Solution of plane triangles No. Three parts specified Formulas for the remaining parts 1 Three sides a b c First method. e b2 c2 - a2 One of the angles is determined by the law of cosines cos a . 2bc Then either the law of sines or the law of cosines is applied. Second method. One of the angles is determined by trigonometric angle formulas. Further proceed in a similar way. Remark. The sum of lengths of any two sides must be greater than the length of the third side. 2 Two sides a b and the included angle 7 First method. The side c is determined by the law of cosines c f a2 b2 - 2ab cos 7. The angle a is determined by either the law of cosines or the law of sines. The angle 3 is determined from the sum of angles in triangle 3 180 - a - 7. Second method. a 3 is found from the sum of angles in triangle a 3 180 - 7 a - 3 is found from the law of tangents tan a _ 3 7 cot Y. 2 a b 2 Then a and 3 can be found. The third side c is determined by either the law of cosines or the law of sines. 3 A side c and the two angles a 3 adjacent to it The third angle 7 is found from the sum of angles in triangle 7 180 - a - 3. Sides a and b are determined by the law of sines. 4 Two sides a b and the angle a opposite one of them The second angle is determined by the law of sines sin 3 sin a. The third angle is 7 180 - a - 3. . The third side is determined by the law of sines c a sm Y . sin a Remark. Five cases are possible 1. a b . the angle is opposite the greater side. Then a 3 3 90 the larger angle is opposite the larger side and the triangle is determined uniquely. 2. a b . the triangle is isosceles and is determined uniquely. 3. a b and b sin a a. Then .

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