I'm reading about algebra and the man most associated with its creation or popularisation, Muhammad al-Khwarizmi. We know that algebra comes from the Arabic "al-jabr", but what I don't understand is why a Persian mathematician would write a treatise in Arabic.
Obviously, I'm thinking in terms of modern times, and that Arabs aren't Persians. Arabs speak Arabic, and Persians speak, well, Persian, or Farsi, known by other names in nearby countries.
What's the reason that a Persian man living between 780 – 850 AD would write in Arabic? Is it because the Persian lands were administrated by Arab-speaking people and therefore Arabic was the official language? Or was it more that Arabic was the language of academia and the educated, much like Mediaeval Latin in Europe or Greek in other places in history?
Also as a follow-up question, the word "algorithm" also comes from this man:
The Arabic source, al-Ḵwārizmī was a name given to the 9th-century mathematician Abū Ja‘far Muhammad ibn Mūsa, author of widely translated works on algebra and arithmetic.
Oxford Living Dictionaries
It's said that the word comes from an Arabic source. So again, why did a Persian man have an Arabic name? Or was that just the Arabic name given to him?