Algebra · a Light

The man who freed algebra also wrote about underground water

Al-Karaji worked in Baghdad around the year 1000. Before him algebra was tied to geometry, because a square meant an area and a cube meant a volume, and a fourth power meant nothing anyone could draw. He cut the tie, treating the powers of the unknown as a ladder you can climb in either direction, with reciprocals going down, and gave rules for multiplying and dividing them. He set out the triangle of binomial coefficients that Europe would later name after Pascal, supported by reasoning historians describe as an early form of mathematical induction. He then left the capital and wrote a manual on locating groundwater and digging qanats, the underground channels that watered Iran, thought to be the oldest surviving text on the subject.

Al-Karaji · Baghdad, c. 953-1029 CE