Re: Plot results not right

*To*: mathgroup at smc.vnet.net*Subject*: [mg89894] Re: Plot results not right*From*: Igor <pischek at gmx.net>*Date*: Tue, 24 Jun 2008 03:26:20 -0400 (EDT)

Hi BrenB, you have to rewrite the function as follows: 2 x - 3 (x^2)^(1/3) + 4 and you will get your plot. The issue is that you get imaginary numbers for x<0 due to the term x^(2/3). By rewriting this term as (x^2)^(1/3) (which algebraically is the same) you force Mathematica to first evaluate the square and then the third root. By doing so, the radicand is always positive, even for x<0, and the third root can be calculated. > 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 >