A question about $Assumptions
- To: mathgroup at smc.vnet.net
- Subject: [mg68909] A question about $Assumptions
- From: "Led" <zep.led at laposte.net>
- Date: Wed, 23 Aug 2006 07:15:22 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Mathematica 5.2 (Windows) gives:
In[1]:=
Integrate[ Cos[m*x] * Cos[n*x] ,{x,0,Pi}]
Out[1]=
\!\(\(m\ Cos[n\ Ï?]\ Sin[m\ Ï?] - n\ Cos[m\ Ï?]\ Sin[n\ Ï?]\)\/\(m\^2 -
n\^2\)\)
which is the expected result. But if instead one writes
In[1]:=
$Assumptions={{m,n}â??Integers};
Integrate[ Cos[m*x] * Cos[n*x] ,{x,0,Pi}]
Out[1]=
0
the result is correct only if m~=n.
What's the problem with $Assumptions?
Shouldn't it be used that way?
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