see http://www.math.utexas.edu/pipermail/maxima/2013/031500.html
Example.
Solve , without i equation x^3-3*x-1=0.
(%i1) eq:x^3-3*x-1=0$
(%i2) solve(eq)$
(%i3) map(rhs,%)$
(%i4) pf(x):=map(polarform,x)$
(%i5) map(pf,%th(2));
(%o5)
[%e^((5*%i*%pi)/9)+%e^(-(5*%i*%pi)/9),%e^((7*%i*%pi)/9)+%e^(-(7*%i*%pi)/9),%e^((%i*%pi)/9)+%e^(-(%i*%pi)/9)]
(%i6) sol:sort(rectform(%));
(%o6) [2*cos(%pi/9),2*cos((5*%pi)/9),2*cos((7*%pi)/9)]
(%i7) float(sol);
(%o7) [1.879385241571817,-0.34729635533386,-1.532088886237956]
(%i8) allroots(eq);
(%o8) [x=-0.34729635533386,x=-1.532088886237956,x=1.879385241571817]
Problem for Maple or Mathematica users: get symbolic solution sol.
I think that Maxima does this better than Maple or Mathematica.
best
Aleksas Domarkas