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MathGroup Archive 2007

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Re: Overly complicated reductions?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg77626] Re: Overly complicated reductions?
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Thu, 14 Jun 2007 05:20:13 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <f4om08$7bj$1@smc.vnet.net>

David Rees wrote:
> Consider f(x)=e^(-2x)
> 
> I wanted to retreive the inverse function f^-1(x), Mathematica to the 
> rescue:
> \!\(Reduce[y == E\^\(\(-2\) x\), x]\)
> 
> \!\(C[1] \[Element] Integers && y != 0 &&
> x == 1\/2\ \((2\ \[ImaginaryI]\ \[Pi]\ C[1] + Log[1\/y])\)\)
> 
> This can't be right, I can rearrange it to just Ln(x)/-2 on paper. What did 
> I do wrong?
> 
> Thanks

You could specify a domain to get something closer to what you are 
looking for. For instance,

In[1]:= Reduce[y == E^(-2*x), x, Reals]

Out[1]= y > 0 && x == (1/2)*Log[1/y]

Regards,
Jean-Marc


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