RE: Exact real solutions of cubic equations

*To*: mathgroup at smc.vnet.net*Subject*: [mg46989] RE: [mg46932] Exact real solutions of cubic equations*From*: JonasB at iui.se*Date*: Fri, 19 Mar 2004 01:35:38 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Thank you all. Within 24 hours I had 10 answers to my question (ComplexExpand), with pointers to the theory and a bit of history. As a newcomer to this list, I am impressed. Jonas > -----Original Message----- > From: JonasB at iui.se [mailto:JonasB at iui.se] To: mathgroup at smc.vnet.net > Sent: den 17 mars 2004 01:55 > To: mathgroup at smc.vnet.net > Subject: [mg46989] [mg46932] Exact real solutions of cubic equations > > > Hello, > > I would like to find the _exact_ real roots of some cubic > polynomials. Mathematica seems to have problems determining > that a root is real > > Solve[1 + a s + b s^2 + s^3 == 0, s] > > results in three complex solutions for a = -4 and b = 3. > FullSimplify does not help, either it does nothing or it gets > stuck, depending on the values of a and b. I can of course > evaluate the solution numerically, but that is not what I > want. Does anyone know of a package that can simplify > expressions with complex numbers? > > Jonas >