Ferrari, the discoverer of the solution, or root, of the quartic equation (fourth-degree polynomial equation), defends his teacher Cardano in a debate in Milan with Tartaglia in 1548.
The debate was provoked by Cardano’s publication three years earlier of Tartaglia's solution of the cubic equation (third-degree equation), which Tartaglia, having solved it in 1535, had confided to Cardano on the condition that it not be published.
This debate brings Ferrari public attention and gains for him a position as tax assessor in Mantua.