Dar Bayan-i ?Istikhradj-i Djayb-i Yik Daradja is a Persian treatise by an anonymous author. The author’s purpose is to describe and explain a method for the determination of the Sine of one degree according to ??sh ch?’s Persian commentary on Ulugh Beg’s Z?dj, and ????z?da’s Arabic treatise entitled Ris?la fi ?Istikhradj Djayb Daradja Wahida. Kad?zada’s work, extant in several manuscripts, is, in fact, a revision of the lost work of the real inventor of the method, Kashani(al-Kashi). Kush ch? in his commentary explains Kashan?’s method, without mentioning his name.
In this article Dar Bayan-i ?Istikhradj-i Djayb-i Yik Daradja is rewritten based on its unique manuscript, so that one can follow the traces of author’s citations from ??sh ch? and Kad?zada’s works.
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