Ahmed ibn Yusuf ibn Ibrahim ibn Tammam alsiddiq AlBaghdadi also known as Abu Ja'far Ahmad ibn Yusuf and Ahmed ibn Yusuf almisri (835  912) was an Arab mathematician, like his father Yusuf ibn Ibrahim (Arabic يوسف بن ابراهيم الصدَيق البغدادي ).
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Ahmed ibn Yusuf was born in Baghdad (today in Iraq) and moved with his father to Damascus in 839. He later moved to Cairo, but the exact date is unknown: since he was also known as alMisri, which means the Egyptian, this probably happened at an early age. Eventually, he also died in Cairo. He probably grew up in a strongly intellectual environment: his father worked on Mathematics, Astronomy and Medicine, produced astronomical tables and was a member of a group of scholars. He achieved an important role in Egypt, which was caused by Egypt's relative independence from the Abbasid Caliph.
For some of the work attributed to Ahmed, it is not exactly clear whether he wrote his, whether his father wrote it or whether they wrote it together. It is clear, however, that he worked on a book on ratio and proportion. This was translated to Latin by Gherard of Cremona and was a commentary of Euclid's Elements. This book influenced early European mathematicians such as Fibonacci. Further, in On similar arcs, he commented on Ptolemy's Karpos (or Centiloquium); many scholars believe that ibn Yusuf was in fact the true author of that work.^{[1]} He also wrote a book on the astrolabe. He invented methods to solve tax problems that were later presented in Fibonnacci's Liber Abaci. He was also quoted by mathematicians such as Thomas Bradwardine, Jordanus de Nemore and Luca Pacioli.
