Solving equations / real valued variables and parameters

• To: mathgroup at smc.vnet.net
• Subject: [mg33985] Solving equations / real valued variables and parameters
• From: hannes.egli at uni-greifswald.de (Hannes Egli)
• Date: Thu, 25 Apr 2002 03:00:07 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```Hi

I have got two questions.

(1)

If I try to solve the following equation for "m".

Solve[a/(a+b+n)-(a+b+n)*((a/(a+b+n))^a)*(((b+n)/(a+b+n))^(b+n))*m^(a+b+n-1)
= = 0, m]

I receive the error message "The equations appear to involve the
variables to be solved for in an essentially non-algebraic way".

However, if I set n=0,

Solve[a/(a+b)-(a+b)*((a/(a+b))^a)*((b/(a+b))^b)*m^(a+b-1) = = 0, m]

Mathematica gives me a solution for "m".

m -> ((((a/(a+b))^a)*((b/(a+b))^b)*(a+b)^2)/a)^(1/(1-a-b))

I do not understand, why Mathematica does not give me a solution for
the first equation, since both equations look very similar.

(2)

My second question concerns real valued variables/parameters. Is there
a possibility to tell Mathematica (at the beginning of a notebook file
or within a function) that some variables and/or parameters are real
valued?