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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
>


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