In treating each of his 14 cases, Khayyam was aware that a cubic might possess two positive roots,depending on how the conics involved intersect.Bold as he was,he ignored negative and repeated roots.He also failed to discover the possibility of three roots occurring,as with an equation of the type x3 + qx = px2 + r (one concrete example being x3 + 11x = 6x2 + 6 ).Khayyam also erroneously concluded that it is not possible to find an algebraic solution of the general cubic .But this should not detract from his mastery of the geometrical theory of third-degree equations,which may be regarded as the most successful accomplishment of an Arabic mathemartician.