1. The "Quartic Formula"  
   Helmut Knaust, S.O.S MATHematics
2. Quartic Equation  
   Eric W. Weisstein, MathWorld, Wolfram Research Inc., Champaign, IL  
3. Quartic equation  
   From Wikipedia, the free Encyclopedia, Wikimedia Foundation  
4. The Quartic Equation  
   Eric S. Rowland, Math. Dept., Rutgers University, Piscataway, NJ
5. Quadratic, cubic and quartic equations  
   School of Mathematics and Statistics, University of St. Andrews, Scotland      
6. Notes on Circulant Matrices and Roots of Small Degree Polynomials  
   Rob Rostermundt, Math. Dept., University of Colorado, Denver, CO  
7. Solving Quartics and Cubics for Graphics  
   Don Herbison-Evans, Computer Science Dept., University of Sydney, Australia
8. Polynomial equations and symmetric functions  PDF  
   Olga Holtz, Math. Dept., University of California-Berkeley, CA  
9. The solution of cubic and quartic equations  PDF  
   Rod Gow, Math. Dept., University College Dublin, Ireland  
10. Solving Polynomial Equations - Ferrari and the Biquadratic  PDF  
    Bill Cherowitzo, Math. Dept., University of Colorado, Denver, CO  

(c) John H. Mathews 2006