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Re: Not all points plot on my graph...
*To*: mathgroup at smc.vnet.net
*Subject*: [mg105206] Re: Not all points plot on my graph...
*From*: Bill Rowe <readnews at sbcglobal.net>
*Date*: Tue, 24 Nov 2009 05:49:39 -0500 (EST)
On 11/23/09 at 6:49 AM, davidfrick2003 at yahoo.com (davef) 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?
When you say f[-3] evaluates to 1, did you actually evaluate
this with Mathematica or in your head? On my system
In[6]:= f[-3] // N
Out[6]= -0.5+0.866025 I
That is Mathematica is not evaluating f[-3] to 1 as you suggest
which explains the missing points. Mathematica by default is not
restricted to real solutions nor does Mathematica give priority
to a real over a complex solution when both exist.
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