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Trigonometry

Ibn Muʿādh al-Jayyānī is one of the several Islamic mathematicians on whom the law of sines is attributed; he wrote " The Book of Unknown Arcs of a Sphere " in the 11th century. This formula relates the lengths of the sides of any triangle, rather than only right triangles, to the sines of its angles. According to the law,

where a, b, and c are the lengths of the sides of a triangle, and A, B, and C are the opposite angles (see figure).