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Re: Cube root of -1 and 1

  • To: mathgroup at smc.vnet.net
  • Subject: [mg90890] Re: Cube root of -1 and 1
  • From: Alberto Verga <Alberto.Verga at laposte.net>
  • Date: Mon, 28 Jul 2008 07:53:12 -0400 (EDT)
  • References: <g6h5fm$h26$1@smc.vnet.net>

On Jul 27, 8:44 am, Bob F <deepyog... at gmail.com> wrote:
> Could someone explain why Mathematica evaluates these so differently?
>
> In[53]:=
>
> (Sqrt[36] - 7)^(1/3)
> (Sqrt[36] - 5)^(1/3)
>
> Out[53]= (-1)^(1/3)
>
> Out[54]= 1
>
> In other words why isn't (-1)^1/3 expressed as -1 ??
>
> Thanks...
>
> -Bob

Because
In[1]:= Solve[x^3 == -1, x]

Out[1]= {{x -> -1}, {x -> (-1)^(1/3)}, {x -> -(-1)^(2/3)}}

A.V.


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