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Ahmad ibn 'Abdallah Habash Hasib Marwazi (796 - d. after 869 in Samarra, Iraq ) was a Persian〔http://www.usc.edu/schools/college/crcc/private/cmje/heritage/History_of_Islamic_Science.pdf〕 astronomer,〔''Islamic Desk Reference'', ed. E. J. Van Donzel, (Brill, 1994), 121.〕 geographer, and mathematician from Merv in Khorasan who described first time Trigonometric ratios: SIN, COS, TAN & COT. He flourished in Baghdad, and died a centenarian after 869. He worked under the Abbasid caliphs al-Ma'mun and al-Mu'tasim. ==Work== He made observations from 825 to 835, and compiled three astronomical tables: the first were still in the Hindu manner; the second, called the 'tested" tables, were the most important; they are likely identical with the "Ma'munic" or "Arabic" tables and may be a collective work of al-Ma'mun's astronomers; the third, called tables of the Shah, were smaller. Apropos of the solar eclipse of 829, Habash gives us the first instance of a determination of time by an altitude (in this case, of the sun); a method which was generally adopted by Muslim astronomers. In 830, he seems to have introduced the notion of "shadow," umbra (versa), equivalent to our tangent in trigonometry, and he compiled a table of such shadows which seems to be the earliest of its kind. He also introduced the cotangent, and produced the first tables of for it.〔(【引用サイトリンク】url=http://www.britannica.com/EBchecked/topic/605281/trigonometry )〕〔Jacques Sesiano, "Islamic mathematics", p. 157, in 〕 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「Habash al-Hasib al-Marwazi」の詳細全文を読む スポンサード リンク
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