Just to add to the options, since Macsyma was mentioned too
With Reduce (available via sourceforge) I can try
on rounded;
precision 5;
equation := impedance = 1/(2*pi*frequency*capacitance);
capacitance := 1.0e-6;
if not numberp impedance then first solve(equation, impedance);
if not numberp frequency then first solve(equation, frequency);
if not numberp capacitance then first solve(equation, capacitance);
end;
and my output is then
12
0.159155
equation := impedance=-----------------------
capacitance*frequency
capacitance := 0.000001
159155.0
impedance=-----------
frequency
159155.0
frequency=-----------
impedance
=====
I think that from outside the immediate community I would characterise
Axiom/Fricas as a sensible choice for those concerned with avoiding
getting wrong answers because of "special cases" or slips that could
emerge from failing to be aware of the detailed mathematics theories and
structures that underpin a calculation. Axiom rather than Fricas may
especially appeal to those who want to ability to inspect its (literate)
source and based on that check and follow through everything it does so
that they can formalise a justification of the correctness of its results.
Arthur
