Abū Sahl al-Qūhī
Abu Sahl ibn Rustam al - Waidschan Quhi, also al - Kuhi (Arabic أبو سهل ويجن بن رستم القوهي, DMG Abū Sahl b Waiǧan Rustam al - Qūhī; . Persian ابوسهل بیژن کوهی, DMG Abu - Sahl Kuhi Bizan; * 940 from Quh in Tabaristan, Iran, † 1000 ) was a Persian astronomer and mathematician.
Al- Quhi was next to Abu l - Wafa and al- Sidschzi an important astronomer and mathematician who lived at whose court in Baghdad during the time of the takeover by the Buyids dynasty. 969/970 he made with as- Sidschzi and others on the orders of the Caliph al-Dawla Adud observations of the winter and summer solstice in Shiraz. Even under the successor caliphs Sharaf al-Dawla ( who reigned from 983 ) he was at the court in Baghdad and made by order of the Caliph in a newly built observatory ( inaugurated in 988 ) in the palace gardens of the Caliph in Baghdad planetary observations. Only a year later joined the observatory with the death of the caliph, which heralded a period of decline of the dynasty.
Al - Quhi is known primarily for his work in geometry, in which he continued the tradition of the ancient Greek mathematician Euclid in addition to, among others, Apollonius and Archimedes. For example, he solved a problem similar to the problems raised by Archimedes in his treatise on the Sphere and Cylinder: you find at given spherical segments A, B is a spherical segment with the same volume as B and the same area as A. The solution the intersection of a hyperbola used with a parabolic. He also completed the construction of the regular heptagon in a traditional Arab, going back to Archimedes treatise. Another problem he solved was the writing of an equilateral pentagon in a square, which leads to the solution of an equation of degree 4 .. He also wrote a treatise on the astrolabe, in which he solved some difficult problems figure, and a treatise about the perfect compass, a device for the construction of conics with application to the construction of astrolabes and sundials.
From al - Quhi also the correspondence with the high-ranking officials, Abu Ishaq al- Sabi is obtained, which was interested in mathematics.