Re: Plot results not right

*To*: mathgroup at smc.vnet.net*Subject*: [mg89925] Re: Plot results not right*From*: Peter Breitfeld <phbrf at t-online.de>*Date*: Tue, 24 Jun 2008 03:32:13 -0400 (EDT)*References*: <g3nhbc$g6$1@smc.vnet.net>

BrenB schrieb: > I'm new to Mathematica. > > 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? > > Thanks > Mathematicas Power uses the principal branch for rational Powers. So e.g. (-1)^(2/3)==-1/2+I Sqrt[3]/2. This is complex and will not be plotted. You may write your own function as a replacement for Power to take a real branch if possible: ------------------- Attributes[ReellePotenz]={Listable, NumericFunction, OneIdentity}; ReellePotenz[b_?Negative, Rational[m_,n_?OddQ]] := (-(-b)^(1/n))^m; ReellePotenz[x__]:=Power[x] ------------------- Then Plot[2 x - 3 ReellePotenz[x, 2/3] + 4, {x, -1, 6}] will give you the plot you expected. Gruss Peter -- ==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-== Peter Breitfeld, Bad Saulgau, Germany -- http://www.pBreitfeld.de