# Why is Brahmagupta considered a great mathematician

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Surname: Brahmagupta

Born: around 598 in the northwest of what is now India

Died: around 670 probably in Ujjain (India)

Teaching / research areas: Number theory, algebra, geometry, astronomy

Brahmagupta was a 7th century Indian astronomer and mathematician. His main work Brahmasphutasiddhanta had a great influence on the Arab scholars and his findings later found their way into medieval Europe through translations from Arabic. Brahmagupta can be called the discoverer of the number zero. He also expanded mathematics to include arithmetic, algebra and geometry, three of which bear his name: the Brahmagupta identity, the Brahmagupta's theorem and the Formula of Brahmagupta.

#### Life

Brahmagupta was born around 600 in the northwest of what is now India. He headed the astronomical observatory in Ujjain and in this capacity wrote several papers on mathematics and astronomy, of which Brahmasphutasiddhanta (in German about "beginning of the universe") is the most famous. As was customary in India back then, it is written in verse.

#### The discovery of the number zero

The Brahmasphutasiddhanta is the first known text in which the zero is treated as a separate number (previously the zero was only used as a placeholder). In contrast to modern mathematics, in which quotients with the divisor 0 are not defined, Brahmagupta also allowed division by 0. He established rules for calculating with zero, positive and negative numbers, which are largely our modern understanding correspond.

#### The Brahmagupta Identity

In Brahmasphutasiddhanta, Brahmagupta also provides the one named after him Brahmagupta identity (also Brahmagupta – Fibonacci identity), which describes how the product of two sums, each consisting of two square numbers, can again be represented as the sum of two other square numbers. It is:

\ ((a ^ 2 + b ^ 2) (c ^ 2 + d ^ 2) = (ac + bd) ^ 2 + (ad-bc) ^ 2 = (ac-bd) ^ 2 + (ad + bc) ^ 2 \)

From the identity it follows directly that the product of two sums of squares is again a sum of squares.

#### On the geometry of quadrilateral tendons: Brahmagupta's theorem and formula

Two other famous results of Brahmagupta concern the geometry of quadrilateral tendons. The Brahmagupta's theorem describes a side bisection in certain quadrilateral tendons and with the Formula of Brahmagupta calculate the area of ​​an arbitrary chordal quadrilateral.

As an astronomer, Brahmagupta made calculations on the position of celestial bodies and on the explanation of solar and lunar eclipses.