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MathGroup Archive 2002

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Re: Replace variable in a function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg37230] Re: Replace variable in a function
  • From: BobHanlon at aol.com
  • Date: Thu, 17 Oct 2002 00:09:25 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

In a message dated 10/16/2002 3:05:57 PM, lcfg3 at yahoo.com writes:

>I´m new, so I´m sorry if the question is so easy, I really think that
>is easy, but I don´t know how to do it.
>
>I have this:
>
>b=n-m
>
>a=x-b
>
>Y=3a + 4a^2
>
>and the program show me this:
>3(x-n+m) + 4(x-n+m)^2
>
>or, something like that, the problem is that I want the program show
>me Y in function of b, or sometimes in function of a, something like
>this:
>
>Y=3(x-b) + 4(x-b)^2
>
>or
>
>Y=3a + 4a^2
>

Solve[{b == n - m, a == x - b, Y == 3a + 4a^2}, Y]

{{Y -> a*(4*a + 3)}}

Solve[{b == n - m, a == x - b, Y == 3a + 4a^2}, Y, a] //
  FullSimplify

{{Y -> (4*b - 4*x - 3)*(b - x)}}


Bob Hanlon


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