Re: Inverse function warnings

*To*: mathgroup at smc.vnet.net*Subject*: [mg99237] Re: [mg99164] Inverse function warnings*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Thu, 30 Apr 2009 06:25:23 -0400 (EDT)*Reply-to*: hanlonr at cox.net

eqn = 3^(2 x) - 12 (3^x) + 27 == 0; Quiet[Solve[eqn, x]] {{x -> 1}, {x -> 2}} Off[Solve::ifun] Solve[eqn, x] {{x -> 1}, {x -> 2}} {Reduce[eqn, x, Reals] // ToRules} {{x -> 1}, {x -> 2}} {Reduce[{eqn, Element[x, Reals]}, x] // ToRules} {{x -> 1}, {x -> 2}} Reduce[eqn, x] Element[C[1], Integers] && (x == 1 + (2*I*Pi*C[1])/Log[3] || x == 2 + (2*I*Pi*C[1])/Log[3]) This indicates that there are an infinite number of solutions. For any integer n Simplify[eqn /. x -> 1 + 2 I*Pi*n/Log[3], Element[n, Integers]] True Simplify[eqn /. x -> 2 + 2 I*Pi*n/Log[3], Element[{n}, Integers]] True Bob Hanlon ---- davef <davidfrick2003 at yahoo.com> wrote: ============= When I execute this in Mathematica 7: Solve[3^(2 x) - 12 (3^x) + 27 == 0, x] I get this: Solve::ifun: Inverse functions are being used by Solve, so some solutions may not be found; use Reduce for complete solution information. >> {{x->1},{x->2}} 1 amd 2 are proper solutions but is it possible to avoid the warning? If I use Reduce: Reduce[3^(2 x) - 12 (3^x) + 27 == 0, x] I get a set of 1 and 2 added to some imaginary number terms that I don't quite understand. I guess my question is: why would the use of inverse functions be so unreliable a solution as to necessitate a warning? And in the interest of clean output, can the warning be supressed other than by deleteing the cell? Thanks