Abu'l Abbas al-Fadl ibn Hatim Al-Nayrizi(about 865 in possiblyNayriz,Iran- about 922 in possiblyBaghdad, Iraq)
Al-Nayrizi was probably born in Nayriz which was a small town southeast ofShiraz now in central Iran. Certainly he must have been associated with this town in his youth to have been called al-Nayrizi. Little is known of his life but we do know that he dedicated some of his works to al-Mu'tadid so he almost certainly moved to Baghdad and worked there for the caliph.
The period during which al-Nayrizi was growing up was a turbulent one in the region in which he lived. Following the assassination of the caliph al-Mutawwakil in 861 there was a period of anarchy and civil war. The Caliph al-Mu'tamid and his brother al-Muwaffaq, who was a military leader, reunited the empire from 870 but a rebellion was eventually put down in 883 only after many years of military campaigns by al-Muwaffaq and his brother al-Mu'tadid. Al-Mu'tamid died in 892 and, since al-Mu'tadid had forced him to disinherit his own son, al-Mu'tadid became caliph in that year.
Al-Mu'tadid reorganized the administration and reformed finances, and he demonstrated great skill and ruthlessness in dealing with the many factions that had arisen. There followed a period of great cultural activity, withBaghdad home to many intellectuals. Al-Nayrizi must have worked for al-Mu'tadid during his ten year of rule, for he wrote works for the caliph on meteorological phenomena and on instruments to measure the distance to objects. If al-Mu'tadid's reign had begun with political intrigue then it seemed to end in the same way, the general opinion being that, in 902, al-Mu'tadid was poisoned by his political enemies. Al-Mu'tadid's son al-Muktafi became caliph in 902 and ruled until 908. It seems likely that al-Nayrizi would continue to work in Baghdad for the new caliph since the same support for intellectuals in Baghdad continued.
TheFihrist (Index) was a work compiled by the bookseller Ibn an-Nadim in 988. It gives a full account of the Arabic literature which was available in the 10th century and in particular mentions al-Nayrizi as a distinguished astronomer. Eight works by al-Nayrizi are listed in theFihrist. A later work, written in the 13th century, described al-Nayrizi as both a distinguished astronomer and as a leading expert in geometry.
Al-Nayrizi's works on astronomy include a commentary of Ptolemy'sAlmagest andTetrabiblos. Neither have survived. He is most famous for his commentary onEuclid'sElements which has survived. TheLeiden manuscript referred to in the title of  contains the revision by al-Nayrizi of the second Arabic translation ofEuclid'sElements by al-Hajjaj. The translation by al-Hajjaj has not survived and the article  examines to what extent al-Nayrizi changed the translation, arguing that indeed he made considerable changes. The paper  looks at different manuscripts containing versions of al-Nayrizi's commentary, some in Arabic, one a Latin version.
In dealing with ratio and proportion in his commentary on theElements, al-Nayrizi adopts concepts proposed by al-Mahani who had worked inBaghdad, probably before al-Nayrizi arrived there. Al-Nayrizi wrote a work on how to calculate the direction of the sacred shrine of the Ka'ba in Mecca (to was important for Muslims to be able to do this since they had to face that direction five times each day when performing the daily prayer). In this work he effectively uses the tan function, but he was not the first to use these trigonometrical ideas.
The article  is a translation into Russian of the short treatise by al-Nayrizi onEuclid's fifth postulate. In his work on proofs of the parallel postulate, al-Nayrizi quotes work by a mathematician named Aghanis. Sabra[Biography inDictionary of Scientific Biography (New York 1970-1990)] argues convincingly that Aghanis is the Athenian philosopher Agapius who was a pupil of Proclus and Marinus and taught around 511 AD.
Article by: J J O'Connor and E F RobertsonNotes:
1-S Brentjes, Der Tabit b. Qurra zugeschriebene Zusatz I, 46Û zu Euklid I, 46 in MS Leiden 399, 1, inAmphora (Basel, 1992), 91-120
2- H L L Busard, Einiges über die Handschrift Leiden 399, 1 und die arabisch-lateinische übersetzung von Gerhard von Cremona, inHistory of mathematics (San Diego, CA, 1996), 173-205
3- A Abdurakhmanov and B A Rozenfel'd (trs.), The treatise of al-Fadl ibn Hatim an-Nayrizi on the proof of a well-known postulate of Euclid (Russian),Istor.-Mat. Issled. No.26
Taken from: http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Al-Nayrizi.html