The placeholder Zero and the Arabic number system for example streamlined European math a lot, I don't even know the method for multiplying Roman numerals , it was so inferior that it is nearly forgotten.
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By the way, the Arabic number system was not invented by any Arabs. Observe how Arabic is written from right to left and everyone, Arabs included, writes numbers the other way, from left to right.
The origin of the so-called Arabac numbers, which are clearly superior to Roman and Hebrew numeric notation, was India.
The numbers can be written as follow:
No angles: 0
One angle:1
Two angles:2
Three angles: 3
Four angles: 4
Five angles: six
Six angles: 6
Seven angles: 7 (hence the cross through the upright as the Europeans write 7)
Eight angles: 8 (two boxes)
Nine angles: 9
The Arabs do not write numbers exactly as Westerners do, but the principle is the same. The Arabs discovered these in India/Pakistan, and brought them back.
Al gebra (literally, "the calculation") was used to discover the position of the mihrab/mithrab, the place in every mosque that always faces Mecca. Mohammad once had everyone face Jerusalem, but then he got pissed at some Jews and changed it to Mecca.
Most of modern astronomy, medicine as well as the reintroduction of Aristotle's philosophy was developed in Cordoba, the site of the most intellectual center of learning in the XI Century. All manner of writings were translated from and into Latin, Arabic and even Greek there.