18. BRAHMAGUPTA

(circa 598 – 670 AD)

As the top math-guru of his era, Brahmagupta journeyed into astronomy and trigonometry: trying to evaluate the periodic positions of heavenly bodies. He was a pacesetter too — introducing some of the earliest known symbolical expressions in his treatises on Geometry, Arithmetic and Algebra (similar to, but independent from what Diophantus did 3 centuries prior). Most of his works have not survived; but those that did, showcased his obsession with quadrilaterals. This explains why several contemporary theorems (such as the formula for the area of a cyclic quad), are named after him. But even more notable is that Brahmagupta is credited (alongside: Liu Hui, Zhang Cang, etc.) with depicting decimals, zero and negative numbers as useful mathematical entities. These are evidenced in his textbook titled Brahmasphutasiddhanta. A century after his demise, the astronomer, Muhammad Al-Fazari, safeguarded this work by translating it into Arabic. It was a copy of this translation that Muhammad Al-Khwarizmi used to learn the decimals. He then utilized his acquired knowledge to publish Al-Jam wal-tafriq bi hisal-al-Hind (which means: Addition and Subtraction based on Indian Arithmetic). This catalog by Al-Khwarizmi was later translated to Latin as Algorithmi de numero Indorum, and was sold throughout Europe. Thus, Brahmagupta taught Europeans (and the wider world) the decimal system. His cachet as a mathematician is such that few people realized how profoundly versed he was in astronomy. I remain impressed by the extent his exegesis, Khandakhadyaka, beautifully and eloquently augmented Aryabhata’s flagship: Ardharatrikapaksa. Several scientific concepts are named after Brahmagupta.

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