
 Finding Real Roots of Quartics 
  Quartic equations need to be solved when ray tracing 4th degree surfaces e.g., a torus. 
  Quartics are the highest degree polynomials which can be solved analytically in general by the method of radicals i.e.: operating on the coefficients with a sequence of operators from the set: sum, difference, product, quotient, and the extraction of an integral order root. 
  The signs of each of the quartic coefficients 'a', 'b', 'c', 'd' and the root of the cubic 'y', may be positive or negative, giving 32 possible combinations of signs. 
 wwwstaff.it.uts.edu.au /~don/pubs/quartic.html (3291 words) 
