Re: Complex and Solve

*To*: mathgroup at smc.vnet.net*Subject*: [mg125143] Re: Complex and Solve*From*: Bob Hanlon <hanlonr357 at gmail.com>*Date*: Fri, 24 Feb 2012 00:57:56 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <201202211115.GAA08330@smc.vnet.net>

Actually I should have checked, with version 8 Solve can handle inequalities so either Reduce or Solve works here. $Assumptions = rfe > 0 && l > 0; r = 1; \[Omega] = 300; vrms = 2; irms = 1/2; \[Phi] = 30 Degree; impedance = r + 1/(1/rfe + 1/(I \[Omega] l)) // FullSimplify; voltage = vrms (Cos[\[Phi]] + I Sin[\[Phi]]) // Simplify; Solve[{irms == voltage/impedance, $Assumptions}, {rfe, l}][[1]] // FullSimplify {rfe -> (1/11)*(-7 + 30*Sqrt[3]), l -> (1/600)*(17 - 4*Sqrt[3])} Alternatively, Solve[{irms == voltage/impedance, Im[l] == 0, Im[rfe] == 0}, {rfe, l}][[1]] // FullSimplify {rfe -> (1/11)*(-7 + 30*Sqrt[3]), l -> (1/600)*(17 - 4*Sqrt[3])} Bob Hanlon On Thu, Feb 23, 2012 at 5:46 AM, <howard.lovatt at gmail.com> wrote: > Thanks Bob, > > Your solution is much better than mine. I had no idea that Reduce could be used like you showed. > > Bizarre that Solve and Reduce behave so differently! > > Thanks again, > > -- Howard. > -- Bob Hanlon

**References**:**Complex and Solve***From:*howard.lovatt@gmail.com