Arabic name: Ahmed Ibn Yusuf Ibn Ibrahim Al-Misri Ibn Ad-Daya Ahmed Ibn Yusuf was born in Baghdad and moved to Damascus in 839, then to Cairo, where he died in 912CE. He was a mathematician, like his father Yusuf Ibn Ibrahim. Among his works that brought him fame and influence is his “Treatise on ratio and proportionality”. This was translated into Latin by Gherard of Cremona. It influenced early European mathematicians such as Fibonacci. He also wrote a book on the astrolabe, a predecessor of the octant and the sextant. He invented methods to solve tax problems in Liber Abaci. He was also quoted by mathematicians such as Thomas Bradwardine, Jordanus Nemorarius and Luca Pacioli. His book “On similar arcs” influenced European mathematicians, as Ahmed Ibn Yusuf proves that similar arcs of circles can be equal and not equal. The proof, like that on ratio and proportion, is based on Euclid.
