**Al-Quhi** was an Islamic mathematician who was a leading figure in the revival and continuation of Greek geometry.

- We can deduce from al-Quhi's name that he came from the village of Quh in Tabaristan.
- A great patron of science and the arts, 'Adud ad-Dawlah supported a number of mathematicians at his court in Baghdad, including al-Quhi, Abu'l-Wafa and al-Sijzi.
- These observations of the winter and summer solstices were made by al-Quhi, al-Sijzi and other scientists in Shiraz during 969/970.
- He continued to support mathematics and astronomy so al-Quhi remained at the court in Baghdad working for the new Caliph.
- Sharaf ad-Dawlah required al-Quhi to make observations of the seven planets and in order to do this al-Quhi had an observatory built in the garden of the palace in Baghdad.
- The instruments in the observatory were built to al-Quhi's own design and installed once the building was complete.
- Al-Quhi was made director of the observatory and it was officially opened in June 988.
- We mention later in this article correspondence between al-Quhi and al-Sabi.
- Our description of al-Quhi's life has highlighted his work in astronomy.
- The geometric problems that al-Quhi studied usually led to quadratic or cubic equations.
- If a solution exists, al-Quhi showed that it will have coordinates which lie on a particular rectangular hyperbola that he has constructed.
- Of course, al-Quhi does not express the mathematics in these modern terms but rather in the usual classical geometry of ancient Greek mathematics.
- Next al-Quhi introduces the "cone of the surface" which, after many deductions, leads to showing that the solution has coordinates lying on a parabola.
- In another treatise On the construction of an equilateral pentagon in a known square al-Quhi solves the problem given in the title again using the intersection of two conic sections, this time two hyperbolas.
- The other, which requires the solution of a quartic equation, is the one presented by al-Quhi.
- Indeed al-Quhi did consider the problem of constructing astrolabes in On the construction of the astrolabe.
- There are a number of difficult mapping problems solved by al-Quhi in this work.
- Despite the appearance of the work being of practical use in constructing an astrolabe, it would appear that al-Quhi was more interested in the mathematics for its own sake than he was in giving a practical manual.
- Finally we should mention the correspondence between al-Quhi and al-Sabi which we mentioned above.
- Perhaps the most interesting parts of the correspondence are six theorems given by al-Quhi concerning the centres of gravity of various figures.

Born about 940, Tabaristan (now Mazanderan), Persia (now Iran). Died about 1000.

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Ancient Arab, Astronomy, Origin Iran

**Oâ€™Connor, John J; Robertson, Edmund F**: MacTutor History of Mathematics Archive