Re: plot

*To*: mathgroup at smc.vnet.net*Subject*: [mg110741] Re: plot*From*: Murray Eisenberg <murray at math.umass.edu>*Date*: Sun, 4 Jul 2010 03:09:40 -0400 (EDT)

Why only for x > 1? Your quotient (which has a redundant set of parentheses around its numerator) evaluates to a negative real when x < 1. Take, e.g., x = -3: Sqrt[x - 1] /. x -> -3 // InputForm 2*I (2 x + 1) Sqrt[x + 1] // InputForm (-5*I)*Sqrt[2] (2 x + 1) Sqrt[x + 1)/Sqrt[x - 1] /. x -> -3 // InputForm -5/Sqrt[2] And consider: (2 x + 1) Sqrt[x + 1]/Sqrt[x - 1] // Simplify // InputForm (1 + 2*x)/Sqrt[(-1 + x)/(1 + x)] So if you want the graph to exclude negative x, you'll have to do it explicitly. On 7/2/2010 2:57 AM, agua 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. > -- Murray Eisenberg murray at math.umass.edu Mathematics & Statistics Dept. Lederle Graduate Research Tower phone 413 549-1020 (H) University of Massachusetts 413 545-2859 (W) 710 North Pleasant Street fax 413 545-1801 Amherst, MA 01003-9305