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In the 7th century CE , Brahmagupta developed a formula , now known as Brahmagupta 's formula , for the area of a cyclic quadrilateral ( a quadrilateral inscribed in a circle ) in terms of its sides .
 Brahmagupta, Brahmagupta
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Brahmagupta, Brahmagupta