3rd order equations



On 8/16/2013 5:56 AM, Esben Byskov wrote:
> *Maybe somebody can help.
>
> I have tried to solve the following rather simple equation using maxima:
>
> (%i1) Eq: -2*q^3+3*q-1.357008100494576;
> (%o1)                  - 2 q  + 3 q - 1.357008100494576
>
> (%i2) solve(Eq,q);*
*first mistake.  Solve finds exact solutions. It is unlikely that 
1.35....576 is known exactly, but solve
assumes it is precisely a certain rational number, and goes from there.

try

allroots(Eq);

or

realroots(Eq);    --- for rational approximations of guaranteed error 
bounds.


*