Re: plot

• To: mathgroup at smc.vnet.net
• Subject: [mg110719] Re: plot
• From: Peter Pein <petsie at dordos.net>
• Date: Sat, 3 Jul 2010 08:18:17 -0400 (EDT)
• References: <i0k2jv\$k0f\$1@smc.vnet.net>

```Am Fri, 2 Jul 2010 11:26:08 +0000 (UTC)
schrieb Sunt <sunting.05 at gmail.com>:

> On Jul 2, 2:57 pm, agua <auguayl... at gmail.com> wrote:
> > Hi
> > With  Plot[( (2x+1) Sqrt[x+1] ) / Sqrt[x-1] ,{x,-5,5}]
> > hoped to obtain a graph only for x>1.
> >
> > What happened?
> > regards.
>
> Hi,
> Add PlotRange option in the command Plot like:
> Plot[( (2x+1) Sqrt[x+1] ) / Sqrt[x-1] ,{x,-5,5},PlotRange->{1,100}]
>

or simply type Plot[...,{x,1,5}].

Plot plots whenever the expression to plot is real valued. Use
Mathematica to see that for real x your expression is real valued iff
x<=-1, x==-1/2 or x>1:

In[1]:= Reduce[Im[((2x+1) Sqrt[x+1])/Sqrt[x-1]]==0==Im[x],x]
Out[1]= x<=-1||x==-(1/2)||x>1

P=C2=B2

```

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