Re: problem of evaluating SQRT
- To: mathgroup at smc.vnet.net
- Subject: [mg28000] Re: problem of evaluating SQRT
- From: "Paul Lutus" <nospam at nosite.com>
- Date: Wed, 28 Mar 2001 02:40:28 -0500 (EST)
- References: <99pd51$leb@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
"Pek" <phsoh at alum.mit.edu> wrote in message news:99pd51$leb at smc.vnet.net... > Hi, > > We have a question of how sqrt can be evaluated. > > In[1]:= > Sqrt[x^2] > > Out[1]= > (This part is just sqrt[X^2]) > > Below we expect the result to be zero but it isn't. How can we get the > correct answer in this case? > > In[2]:= > Sqrt[x^2] - x > > Out[2]= > (This part is -x + sqrt[x^2] ) But Mathematica is providing the correct answer. What if x = -1? In this case, Sqrt[(-1)^2] - -1 = 2. You are just not accustomed to thinking in symbolic terms. For Mathematica to process: Sqrt[x^2] - x and return "0", this must be true for all possible values of x. It is only true for positive, real values. -- Paul Lutus www.arachnoid.com