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Re: why does it still running?!

  • To: mathgroup at smc.vnet.net
  • Subject: [mg113164] Re: why does it still running?!
  • From: István Zachar <zac at freemail.hu>
  • Date: Sat, 16 Oct 2010 13:10:53 -0400 (EDT)
  • References: <i9a4v4$nbd$1@smc.vnet.net>

On Oct 15, 8:02 pm, olfa <olfa.mra... at yahoo.fr> wrote:
> Hi Mathematica community,
> why Mathematica still running and so can't give me a solution for this sy=
stem
> Reduce[
> ((1 - a)*x - b)/a^(i/1) == ((1 - a)*y - b)/a^(j/1) && j == 10,{y}=
,
> Backsubstitution -> True]
>
> Thank you very much.

On my machine (2 Intel CPU @ 2.4GHz, 2 GB RAM, Win 7, Mathematica 7.0.1.0) it
produces the output immediately:

In[1]:= Reduce[((1 - a)*x - b)/a^(i/1) == ((1 - a)*y - b)/a^(j/1) &&
  j == 10, {y}, Backsubstitution -> True]

Out[1]= (j == 10 && a == 1 && b == 0) || (j == 10 && (-1 =
+ a) a != 0
&&
    y == -((
     a^-i (-a^10 b + a^i b + a^10 x - a^11 x))/(-1 + a))) || (j ==
    10 && b != 0 && a == 1)


Istvan


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