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Re: Are some equations unsolvable?
Posted:
Sep 13, 2012 3:43 AM


One way to get a result is to rewrite f placing everything into Exp[] like so:
In[1]:= FullSimplify[Log[(1/(sigma*Sqrt[2 Pi]))*Sqrt[(Pi/(1/(2*sigma^2)))]]] Out[1]= 1/2 (Log[sigma]  Log[sigma])
In[2]:= Block[{f, m, sigma}, f = Exp[((m/sigma^2)^2)/4*(1/2*sigma^2) + (m^2/(2*sigma^2)) + 1/2 (Log[sigma]  Log[sigma])]; Solve[f == 216, sigma]]
(*Solve::ifun message*)
Out[2]= {{sigma > (((1)^(1/4) m)/( 2 Sqrt[1/3 (\[Pi] + I Log[46656])]))}, {sigma > ((1)^(1/4) m)/( 2 Sqrt[1/3 (\[Pi] + I Log[46656])])}}
Note that Log[46656] == 2 Log[216].
Perhaps this helps...
"Sergio Sergio" <zerge69@gmail.com> wrote in message news:k2pc54$99t$1@smc.vnet.net... > 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 >



