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Brahmasphutasiddhanta XII.21 (628 CE) gives the exact-area formula for any cyclic quadrilateral with sides a, b, c, d: K = √[(s−a)(s−b) (s−c)(s−d)], where s = (a+b+c+d)/2. First known generalization of Heron's triangle area formula to four sides. Rediscovered in Europe by Carl Strehlke in 1842 — 1,214 years later. Bhaskara II preserved the rule in Lilavati §167 (1150 CE), source of the verbatim quote.

Algebra, with Arithmetic and Mensuration, from the Sanscrit of Brahmegupta and Bháscara · 628