Re: Are some equations unsolvable?

*To*: mathgroup at smc.vnet.net*Subject*: [mg128067] Re: Are some equations unsolvable?*From*: Bob Hanlon <hanlonr357 at gmail.com>*Date*: Thu, 13 Sep 2012 03:38:24 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net*References*: <20120912070044.88F3A6862@smc.vnet.net>

f = (1/(sigma*Sqrt[2 Pi]))*Sqrt[(Pi/(-1/(2*sigma^2)))]* Exp[((m/sigma^2)^2)/4*(-1/2*sigma^2) + (m^2/(2*sigma^2))] (E^((3*m^2)/(8*sigma^2))*Sqrt[-sigma^2])/sigma Solve[f == 216, {m, sigma}, VerifySolutions -> True] Solve::ifun: Inverse functions are being used by Solve, so some solutions may not be found; use Reduce for complete solution information. >> Solve::svars: Equations may not give solutions for all "solve" variables. >> {} There are no solutions. If sigma is a real number then Sqrt[-sigma^2} is complex and f cannot equal 216. Simplify[f, Element[sigma, Reals]] (I*E^((3*m^2)/(8*sigma^2))*Abs[sigma])/sigma Simplify[f, sigma > 0] I*E^((3*m^2)/(8*sigma^2)) Bob Hanlon On Wed, Sep 12, 2012 at 3:00 AM, Sergio Sergio <zerge69 at gmail.com> wrote: > Hi, > This is what I have: > > f = (1/(sigma*Sqrt[2 Pi]))*Sqrt[(Pi/(-1/(2*sigma^2)))]* > Exp[((m/sigma^2)^2)/4*(-1/2*sigma^2) + (m^2/(2*sigma^2))] > > Solve[f == 216, sigma] > > And I get this message: "This system cannot be solved with the methods available to Solve" > > Is it because there is no way to isolate sigma? Or am I doing something wrong? > > Thanks >

**References**:**Are some equations unsolvable?***From:*Sergio Sergio <zerge69@gmail.com>