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Early study of triangles can be traced to the 2nd millennium BC, in Egyptian mathematics (Rhind Mathematical Papyrus) and Babylonian mathematics. Systematic study of trigonometric functions began in Hellenistic mathematics, reaching India as part of Hellenistic astronomy. In Indian astronomy, the study of trigonometric functions flowered in the Gupta period, especially due to Aryabhata (6th century CE). During the Middle Ages, the study of trigonometry continued in Islamic mathematics, hence it was adopted as a separate subject in the Latin West beginning in the Renaissance with Regiomontanus. The development of modern trigonometry shifted during the western Age of Enlightenment, beginning with 17th-century mathematics (Isaac Newton and James Stirling) and reaching its modern form with Leonhard Euler (1748). ==Etymology== The term "trigonometry" was derived from the Greek word "τριγωνομετρία" ("''trigonometria''"), meaning "triangle measuring", from "τρίγωνο" (triangle) + "μετρεῖν" (to measure). Our modern word "sine" is derived from the Latin word ''sinus'', which means "bay", "bosom" or "fold", translating Arabic ''jayb''. The Arabic term is in origin a corruption of Sanskrit ''jīvā'', or "chord". Sanskrit ''jīvā'' in learned usage was a synonym of ''jyā'' "chord", originally the term for "bow-string". Sanskrit ''jīvā'' was loaned into Arabic as ''jiba''.〔Boyer (1991), page 252: ''It was Robert of Chester's translation from the Arabic that resulted in our word "sine." The Hindus had given the name jiva to the half-chord in trigonometry, and the Arabs had taken this over as jiba. In the Arabic language there is also the word jaib meaning "bay" or "inlet." When Robert of Chester came to translate the technical word jiba, he seems to have confused this with the word jaib (perhaps because vowels were omitted); hence, he used the word sinus, the Latin word for "bay" or "inlet."''〕〔 This term was then transformed〔 into the genuine Arabic word ''jayb'', meaning "bosom, fold, bay", either by the Arabs or by a mistake〔 of the European translators such as Robert of Chester (perhaps because the words were written without vowels〔), who translated ''jayb'' into Latin as ''sinus''.〔Boyer (1991), page 252: "It was Robert of Chester's translation from the Arabic that resulted in our word "sine." The Hindus had given the name jiva to the half-chord in trigonometry, and the Arabs had taken this over as jiba. In the Arabic language there is also the word jaib meaning 'bay' or 'inlet.' When Robert of Chester came to translate the technical word jiba, he seems to have confused this with the word jaib (perhaps because vowels were omitted); hence, he used the word sinus, the Latin word for 'bay' or 'inlet.'"〕 Particularly Fibonacci's ''sinus rectus arcus'' proved influential in establishing the term ''sinus''.〔O'Connor (1996).〕 The words "minute" and "second" are derived from the Latin phrases ''partes minutae primae'' and ''partes minutae secundae''. These roughly translate to "first small parts" and "second small parts". 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「History of trigonometry」の詳細全文を読む スポンサード リンク
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