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Re: coefficients of polynomial

  • To: mathgroup at smc.vnet.net
  • Subject: [mg107953] Re: coefficients of polynomial
  • From: dh <dh at metrohm.com>
  • Date: Thu, 4 Mar 2010 05:24:42 -0500 (EST)
  • References: <hmlf1q$jsd$1@smc.vnet.net>

Hi,
Reduce can do this. E.g.:
Reduce[ForAll[{x, y},
   a x^2 + b x y + c y^2 ==
    d (x + y)^2 + e (x - y)^2 + f (x^2 - y^2)], {d, e, f}]
Daniel

On 03.03.2010 11:52, Jim Armstrong wrote:
> Hi,
>
> I am trying to find the coefficients d,e,f of this simple equating:
>
> ax^2+bxy+cy^2=d(x+y)^2+e(x-y)^2+f(x^2-y^2)
>
> I mean I am waiting for this type of solution:
>
> d=(a-b+c)/2
> e=b/2
> f=(a-c)/2
>
> so how can I get these constants?
>
> I searched it and tried to use Solve, Expand...but either they dont give it or they solve it in terms of all terms (a,b,c,x,y).
>
> Thanks a lot
>


-- 

Daniel Huber
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E-Mail:<mailto:dh at metrohm.com>
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