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MathGroup Archive 2001

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Re: Simplyfying expression

  • To: mathgroup at smc.vnet.net
  • Subject: [mg30632] Re: [mg30624] Simplyfying expression
  • From: BobHanlon at aol.com
  • Date: Fri, 31 Aug 2001 19:58:09 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

In a message dated 2001/8/31 4:23:48 AM, 
shusaku.yamamoto at buseco.monash.edu.au writes:

>I have another problem. I tried simplifying the solutions of a
>simultaneous difference equations; i.e. I typed
>
>Simplify[-1-5*(3^x)+(31/63)*(2^(2+x))*(5^(1+x))-((53*(10^x))/63)]
>Simplify[-1-5*(3^x)+(31/63)*(2^(2+x))*(5^(1+x))-((53*(10^x))/63),x "set
>of" Reals]
>FullSimplify[-1-5*(3^x)+(31/63)*(2^(2+x))*(5^(1+x))-((53*(10^x))/63)]
>
>Yet, Mathematica does not simplify the expressions. I know the above
>expression can be written as:
>-1-5*(3^x)+9(10^x).
>

expr=-1-5*3^x+(31/63)*2^(2+x)*5^(1+x)-(53*10^x)/63;

Using brute force

FullSimplify[expr /. 
      2^x_ -> a*2^(x-1 )] /. 
  a -> 2

-1 - 5*3^x + 9*10^x


Bob Hanlon
Chantilly, VA  USA


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