Resaleh fi estekhraj-e jayb-e daraje-ye vahedeh

• Persian Title: رساله فی استخراج جَیب درجه واحده
• Transliterated Title: Risālah fī istikhrāj-i jayb-i darajah-yi wāḥidah
• English Title: Treatise on the Calculation of the Sine of One Degree
• Author: Mūsā b. Muḥammad Qāḍīzādah Rūmī (8th–9th century A.H.)
• Editor & Translator: Fāṭimah Sawādī
• Language: Persian
• ISBN: 978-964-8700-67-1
• Publication Year: 2008 (1387 A.H.)
• Pages: 120
• Format: PDF
• Category: Treatises
• Miras Maktoob Collection Code: 179

【Summary】

The calculation of the sine of one degree was one of the most challenging problems in medieval trigonometry. Ghiyāth al-Dīn Jamshīd Kāshānī (d. 832 A.H.) developed an innovative and highly accurate method for this calculation in a work titled Risālat al-Watar wa al-Jayb, which has unfortunately not survived.
The absence of Kāshānī’s original treatise, combined with Ulugh Beg’s (d. 853 A.H.) claim in the Zīj-i Gūrkānī to have devised a precise method for calculating the sine of one degree, created uncertainty regarding the origins of these techniques.
Qāḍīzādah Rūmī, a close colleague of Kāshānī at the Samarqand observatory, composed Risālah fī istikhrāj-i jayb-i darajah-yi wāḥidah to explain and analyze Kāshānī’s method. This work preserves a detailed account of Kāshānī’s approach and serves as a crucial source for understanding advanced trigonometric computation in the Islamic scientific tradition.