Trigonometry · a Light

His sine table was right to eight decimal places

Abu al-Wafa al-Buzjani came from Khurasan to Baghdad as a young man and stayed for the rest of his life. He treated all six trigonometric quantities as functions rather than as lines in a diagram, gave the addition formula for sines, and computed a fresh table at intervals of fifteen minutes of arc. His value for the sine of half a degree is correct to eight decimal places, and was not improved on for a long time. The spherical law of sines, the rule that makes triangles on a globe calculable, is credited to him and to two contemporaries, Abu Nasr Mansur and al-Khujandi, and which of the three had it first has never been settled. He also wrote a book of geometrical constructions for craftsmen.

Abu al-Wafa al-Buzjani · Baghdad, 940-998 CE