Nasir al-Din al-Tusi's Commentary on Euclid's Elements

Nasir al-Din al-Tusi (1201 – 1274) was a Persian astronomer and mathematician.  He is noted for writing the first major work on pure trigonometry as well as for his commentaries on Greek works.  This is a page from a later Arabic edition of his commentary on Euclid’s Elements, a page dealing with Euclid's method of exhaustion.