title: Brāhmasphuṭasiddhānta
context: The Brāhmasphuṭasiddhānta ("Correctly Established Doctrine of Brahma", abbreviated BSS) is the main work of Brahmagupta, written c. 628.[1] Τhis text of mathematical astronomy contains significant mathematical content, including a good understanding of the role of zero, rules for manipulating both negative and positive numbers, a method for computing square roots, methods of solving linear and quadratic equations, and rules for summing series, Brahmagupta's identity,  and  Brahmagupta’s theorem.
question: When was the  Brāhmasphuṭasiddhānta written?
answers: c. 628