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Re: Not all points plot on my graph...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg105195] Re: Not all points plot on my graph...
  • From: "michael.p.croucher at googlemail.com" <michael.p.croucher at googlemail.com>
  • Date: Tue, 24 Nov 2009 05:47:29 -0500 (EST)
  • References: <hedte4$lsn$1@smc.vnet.net>

On 23 Nov, 11:59, davef <davidfrick2... at yahoo.com> wrote:
> Why is it when I write this...
>
> Clear[f, x]
> f[x_] = (x + 2)^(2/3)
> Plot[f[x], {x, -3, 0}, PlotRange -> {{-3, 0}, {-4, 4}}]
> f[-3]
>
> .. I get no values show in the graph for x<-2 even though f[-3]
> evaluates to (-1)^(2/3).
>
> (-1)^(2/3) evaluates as f[-3]=1 so why wouldn't the point (-3,1) plot
> on my graph?

Hi Dave

f[-3] isn't 1 - it's -0.5 + 0.866025 I and, since this is a complex
number, Mathematica can't plot it on a simply x-y graph  Evaluate

f[-3] //N to see the complex result for yourself

Cheers,
Mike
www.walkingrandomly.com


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