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