# Brahmagupta (c. AD 598–c.665)

Brahmagupta was a Hindu astronomer and mathematician who became the head of
the observatory at Ujjain – the foremost mathematical center of India
at this time; he was the last and most accomplished of the ancient Indian
astronomers. His main work, *Brahmasphutasiddhanta* (The Opening of
the Universe), written in 628, contains some remarkably advanced ideas,
including a good understanding of the mathematical role of zero,
rules for manipulating both positive and negative
numbers, a method for computing square roots, methods of solving linear
and some quadratic equations, and rules
for summing series. His contributions to astronomy were equally ahead of
their time. Brahmagupta's theorem states that in a cyclic quadrilateral
(a four-sided shape whose corners lie on a circle) having perpendicular
diagonals, the perpendicular to a side from the point of intersection of
the diagonals always bisects the opposite side.