Parameters for Plotting a Quartic

The four roots of the reduced quartic equation can be expressed in terms of just three parameters, say , , , where , , are the roots of the resolvent cubic equation , known as Euler's cubic. Note that are the six roots of the resolvent sextic Thus, the key to solving the quartic is to first solve the resolvent cubic

For a more detailed discussion see R. W. D. Nickalls, "The Quartic Equation: Invariants and Euler's Solution Revealed," The Mathematical Gazette, 94, 2009 pp. 66–75.