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 -- > > > >