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AW: System for which Solve and NSolve both fail

• To: mathgroup at smc.vnet.net
• Subject: [mg30588] AW: [mg30572] System for which Solve and NSolve both fail
• From: Matthias.Bode at oppenheim.de
• Date: Thu, 30 Aug 2001 03:51:34 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

Hello Ben,

straight from the Help Browser:

1. "Solve deals primarily with linear and polynomial equations."
2. "NSolve[aa, a, . a, aa, a, . a] solves a system of polynomial equations."


Use FindRoot, it works, I tried it.

Best regards,

Matthias.

-----Ursprungliche Nachricht-----
Von: Ben Langton [mailto:ben at spam.bugs.me.quickmath.com]
Gesendet: Mittwoch, 29. August 2001 07:40
An: mathgroup at smc.vnet.net
Betreff: [mg30572] System for which Solve and NSolve both fail


Hi,

I noticed that Mathematica seems unable to solve this system of equations :

3^x + 3^y = 90

x + y = 6

With a bit of thought, you can see by inspection that the solutions are

{x , y} = {2 , 4} or {4 , 2}

However, when I use the commands

Solve[{3^x+3^y==90,x+y==6},{x,y}]

or

NSolve[{3^x+3^y==90,x+y==6},{x,y}]

I get a warning message starting with

Solve::incnst: Inconsistent or redundant transcendental equation

Can anyone shed some light on what is going on here? Any way to get around
this problem?

(I am using Mathematica v 3.0.0.0 under Mac OS 9.2.1, although I believe a
similar thing occurs under v 4.x)

Regards,

Ben Langton

http://www.quickmath.com/