Groups > comp.soft-sys.math.mathematica > #3085

Re: Replacement faild

From	Bob Hanlon <hanlonr@cox.net>
Newsgroups	comp.soft-sys.math.mathematica
Subject	Re: Replacement faild
Date	2011-06-12 15:03 +0000
Organization	Steven M. Christensen and Associates, Inc and MathTensor, Inc.
Message-ID	<it2kge$e3k$1@smc.vnet.net> (permalink)

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You will not get exact results using inexact numbers (machine precision).

eq1 = -(1104.6607499200002`/(-y + T)^2) + (x (1 + 2 T))/(T + T^2)^2 == 0;

eq2 = 2209.3214998400003`/(-y + T)^3 - 
    x ((2 (1 + 2 T)^2)/(T + T^2)^3 - 2/(T + T^2)^2) == 0;

sol = Solve[Rationalize[eq1 && eq2, 0], {x, y}, Reals][[1]] // Simplify

{x -> (1418800860*(1 + 3*T + 3*T^2)^2)/(1284377*(1 + 2*T)^3), 
   y -> T^3/(1 + 3*T + 3*T^2)}

{eq1, eq2} /. sol // Simplify

{True, True}


Bob Hanlon

---- Math Math <mathematica023@gmail.com> wrote: 

=============
Hi,
I'm new for this forum, and really i'm new for Mathematica also!
I've got this problem: two equation in a system. I use NSolve to have the
solutions of system, but when i try to verify the solutions Mathematica
doesn't give True, but another value.
Can anyone help me?

eq1 = -(1104.6607499200002`/(-y + T)^2) + (x (1 + 2 T))/(T + T^2)^2 == 0 ;
eq2 = 2209.3214998400003`/(-y + T)^3 -x ((2 (1 + 2 T)^2)/(T + T^2)^3 - 2/(T
+ T^2)^2) == 0 ;
sol = NSolve[eq1 && eq2, {x, y}, Reals] // FullSimplify;
eq2 /. sol // FullSimplify
eq1 /. sol // FullSimplify
NSolve::ratnz: NSolve was unable to solve the system with inexact
coefficients. The answer was obtained by solving a corresponding exact
system and numericizing the result. >>
....

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Re: Replacement faild Bob Hanlon <hanlonr@cox.net> - 2011-06-12 15:03 +0000

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