solving cubic/quartic equations non-iteratively

quote:
There are certainly formulas for solving polynomials numerically up to 
4th degree non-iteratively, but you will almost certainly get better 
results using iterative methods.
endquote

I must be missing something here.  Why not use the analytic formulas for 
polynomials below 5th degree?  Once you do so, your answer is as precise 
as the level of precision you enter for the coefficients.