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Re: Why isn't Expand[] grouping terms by order?

• To: mathgroup at smc.vnet.net
• Subject: [mg87859] Re: Why isn't Expand[] grouping terms by order?
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Fri, 18 Apr 2008 07:13:01 -0400 (EDT)
• Organization: Uni Leipzig
• References: <fu9fq7$cbn$1@smc.vnet.net>
• Reply-to: kuska at informatik.uni-leipzig.de

Hi,

because it doen not know that you look for
orders of x and not of a or b ..
and
Collect[Expand[(1 + a*x)*(1 + b*x), x], x]

will do what you want.

Regards
   Jens

p at dirac.org wrote:
> Consider this:
> 
>    In[19]:= Expand[ (1+a*x)*(1+b*x), x]
> 
>                                  2
>    Out[19]= 1 + a x + b x + a b x
> 
> 
> How can I coax Mathematica to give me this, instead:
> 
>                                  2
>    Want[19]= 1 + (a + b) x + a b x
> 
> Why isn't Mathematica reporting the answer in terms of powers of x?
> 
> Thanks!
>