[Date Index]
[Thread Index]
[Author Index]
Re: 1 equals 3 (among others)
*To*: mathgroup at smc.vnet.net
*Subject*: [mg32196] Re: [mg32180] 1 equals 3 (among others)
*From*: Andrzej Kozlowski <andrzej at tuins.ac.jp>
*Date*: Sat, 5 Jan 2002 00:10:35 -0500 (EST)
*Sender*: owner-wri-mathgroup at wolfram.com
With your definition of f[x]
In[4]:=
f[x]
Out[4]=
(1/2)*(4 + Sqrt[(-2 + x)^2] - x)
You seem to be under the illusion that that last expression is 1 for all
values of x. I think you should review some basic school math, in
particular things like:
In[8]:=
Sqrt[(-2)^2]
Out[8]=
2
and so on...
Andrzej Kozlowski
Toyama International University
JAPAN
http://platon.c.u-tokyo.ac.jp/andrzej/
On Friday, January 4, 2002, at 07:03 PM, Grischa Stegemann wrote:
> Dear group
>
> Can anyone explain to me what is going on here? Look at this:
>
> In[1]:=f[x_] = (4 - x + Sqrt[-4*(3 - x) + (x - 4)^2])/2;
> In[2]:=Simplify[-4*(3 - x) + (x - 4)^2]
> Out[2]=(-2 + x)^2
>
> Well, right now we can be pretty sure that f[x]=1 for all x. But
> Mathematica (4.0.2.0X) seems to know better:
>
> In[3]:=Map[f[#1]&, {0, 0.1, 1.7, 2, 2.5, 3}]
> Out[3]={3, 2.9, 1.3, 1, 1., 1}
>
> It took me hours to find this error in my rather complex setting...;-(
>
> Bye, Grischa
> --
> -------------------------------------------------------------------------
> Grischa Stegemann Technische Universit?t
> Berlin --
>
>
>
>
Prev by Date:
**Re: Length and Drop**
Next by Date:
**Re: 1 equals 3 (among others)**
Previous by thread:
**Re: 1 equals 3 (among others)**
Next by thread:
**Re: 1 equals 3 (among others)**
| |