Berggren, J. L. «Innovation and Tradition in Sharaf al-Din al-Tusi's Muadalat». Journal of the American Oriental Society, 110, 2, 1990, p. 304–309. DOI: 10.2307/604533.
J. J. O'Connor and E. F. Robertson (1999), Omar Khayyam, MacTutor History of Mathematics archive, states, "Khayyam himself seems to have been the first to conceive a general theory of cubic equations."
st-andrews.ac.uk
mathshistory.st-andrews.ac.uk
In O'Connor, John J.; Robertson, Edmund F. «Omar Khayyam» (en anglès). MacTutor History of Mathematics archive. School of Mathematics and Statistics, University of St Andrews, Scotland. one may read This problem in turn led Khayyam to solve the cubic equationx3 + 200x = 20x² + 2000 and he found a positive root of this cubic by considering the intersection of a rectangular hyperbola and a circle.
O'Connor, John J.; Robertson, Edmund F. «Sharaf al-Din al-Muzaffar al-Tusi» (en anglès). MacTutor History of Mathematics archive. School of Mathematics and Statistics, University of St Andrews, Scotland.
