Eleven Proof of the Cosinus Form of Two Angle Differences
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Publishing House Education and Science s.r.o.
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This paper presents eleven different methods for proving addition formulas for trigonometric functions. The first methods of proof are given by the seventh trigonometric function defined in Mirzo Ulugbek’s work. Other methods of proof are based on the equality of triangles, formulas for calculating the area of a triangle, the distance between two points, definitions of trigonometric functions, basic trigonometric identities, and operations on vectors.
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Trigonometric functions, saxm(x), circle, basic trigonometric identity, right triangle, Pythagorean theorem, equilateral triangle, surface of a triangle, distance between two points, sum of vectors, scalar product