Re: Plot results not right

*To*: mathgroup at smc.vnet.net*Subject*: [mg89899] Re: Plot results not right*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Tue, 24 Jun 2008 03:27:15 -0400 (EDT)*Organization*: The Open University, Milton Keynes, UK*References*: <g3nhbc$g6$1@smc.vnet.net>

BrenB wrote: > I'm studying Calculus, and I'm trying to reproduce, in Mathematica, > the graph results of an equation in my book. > > Plot[2 x - 3 x^(2/3) + 4, {x, -1, 6}] > > The output graph is correct, except there should be graphing in the > 2nd and 3rd quadrant, and there is none. > > Is there another way to enter this equation into Mathematica to get > the correct graph results? Are you sure that the function you want to plot is this one? I might have missed something, but, since you mentioned you are taking a class in Calculus, I think you are studying real functions of a real variable (i.e. functions from R to R). The function f[x_] := 2 x - 3 x^(2/3) + 4 is defined on R+ only (i.e. for x positive or null) and is positive on this interval. Thus the function is always above the x-axis and can be drawn (or make sense) only for x >= 0. Therefore the graph returned by Plot[] is correct. Regards, -- Jean-Marc