Re: Is -1^(2/5) really undefined in R?

*To*: mathgroup at smc.vnet.net*Subject*: [mg69086] Re: [mg69075] Is -1^(2/5) really undefined in R?*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Wed, 30 Aug 2006 06:32:11 -0400 (EDT)*Reply-to*: hanlonr at cox.net*Sender*: owner-wri-mathgroup at wolfram.com

It appears that you mean (-1)^(2/5) (-1)^(2/5)//ComplexExpand -(1/4) + Sqrt[5]/4 + (1/2)*I*Sqrt[(1/2)*(5 + Sqrt[5])] (-1)^(2/5)//N 0.30901699437494745 + 0.9510565162951536*I Plot[{Re[x^(2/5)],Im[x^(2/5)]},{x,-2,0}, PlotStyle->{Blue,Red}]; Plot[{Re[(-1)^x],Im[(-1)^x]},{x,0,1}, PlotStyle->{Blue,Red}]; Bob Hanlon ---- Ben <ben.carbery at spam.me> wrote: > Is -1^(2/5) really undefined in R? > > Mathematica seems to think so, I guess since it looks like a negative square root, but > > -1^(2/5) = (-1^2)^(1/5) = 1^(1/5) = 1 > > Is this correct mathematically? > > cheers, > > BC >