Trigonometry (from Ancient Greek τρίγωνον (trígōnon) ´triangle´, and μέτρον (métron) ´measure´) is a branch of mathematics concerned with relationships between angles and ratios of lengths. The field emerged ...
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in the Hellenistic world during the 3rd century BC from applications of geometry to astronomical studies. The Greeks focused on the calculation of chords, while mathematicians in India created the earliest-known tables of values for trigonometric ratios (also called trigonometric functions) such as sine.
Throughout history, trigonometry has been applied in areas such as geodesy, surveying, celestial mechanics, and navigation.