The Arab astronomer Abu Ja'far Muhammad ibn Musa Al-Khwarizmi was the author of about a half dozen astronomical works, including a book entitled Al-jabr w'al muqabala (written in 830 AD) that gave the name al-jabr to the branch of mathematics that is now known by its modern spelling as algebra.

The word al-jabr is usually translated as "restoring," with reference to restoring the balance in an equation by placing on one side of an equation a term that has been removed from the other. For example, given the equation x²-5=4, a balance is restored by writing x²=9. The second part of the title, al muqabala, probably meant "simplification," as in the case of combining 2x+5x to obtain 7x, or by subtracting out equivalent terms from both sides of an equation.

Al-Khwarizmi's algebra was based on the earlier work of the Hindu mathematician Brahmagupta (b. 598), but also contained...