Re: Different answers in mathematica and my calculator.

*To*: mathgroup at smc.vnet.net*Subject*: [mg125586] Re: Different answers in mathematica and my calculator.*From*: DrMajorBob <btreat1 at austin.rr.com>*Date*: Tue, 20 Mar 2012 02:20:11 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <201203191000.FAA01033@smc.vnet.net>*Reply-to*: drmajorbob at yahoo.com

-1 has three cube roots, so your expression has three possible results, all of them correct: Solve[x^3 == -1, x] % // ComplexExpand 4/(3 x) /. % {{x -> -1}, {x -> (-1)^(1/3)}, {x -> -(-1)^(2/3)}} {{x -> -1}, {x -> 1/2 + (I Sqrt[3])/2}, {x -> 1/2 - (I Sqrt[3])/2}} {-(4/3), 4/(3 (1/2 + (I Sqrt[3])/2)), 4/(3 (1/2 - (I Sqrt[3])/2))} Hence, it's not the least surprising if your calculator gives a different result than Mathematica. I do think the Solve result above (before applying ComplexExpand) is less than ideal or complete since, as I said before, -1 has three cube roots, leaving two of the reported solutions ambiguous. Mathematica chooses a specific "branch" of the multivalued cube-root function. Bobby On Mon, 19 Mar 2012 05:00:46 -0500, Nile <thrasher300 at gmail.com> wrote: > 4/(3Power[2(-2)+3, (3)^-1]) > > I get -(4/3) (-1)^(2/3) in Mathematica but only -4/3 on my calculator. > > > N[Sec[8/(8 Sqrt[2])]]/Degree to get Cos^-1 of 8/(8 Sqrt[2]) and it gives > me 75 deg instead of 45... > > I'm not sure what I'm doing wrong, I tried in Wolfram Alpha and it gives > me the same thing. > > Thank you. > > -Francis > -- DrMajorBob at yahoo.com

**References**:**Different answers in mathematica and my calculator.***From:*Nile <thrasher300@gmail.com>