# RE: weird eqns

*To*: mathgroup@smc.vnet.net*Subject*: [mg10781] RE: [mg10698] weird eqns*From*: R Finley <trfin@umsmed.edu>*Date*: Thu, 5 Feb 1998 00:58:27 -0500

Hi Troy, Like so many problems in Mathematica, you often need to manipulate a bit to get the answer you want, rather than simply blindly plugging things in. And even if you can get an answer by blindly plugging things in, if you haven't played around with the equations with pencil and paper you will likely get blindsided with an unexpected (ie wrong) answer. Playing around with your equations it is clear that they have such large exponents that it makes them rather unstable to a direct numerical attack unless you have some idea in advance where you are looking. If you label your constants as: alpha 38530, beta 6, gamma .987*2.303, delta 3000, and epsilon 167 then you are really interested in the region where the exponent of 10 is close to zero. You can find this using: NSolve[ -(alpha + delta) + (beta + epsilon) t Ð0, t] Which gives the solution t-> 27.9301 If you rearrange your equations you can use FindRoot to get the more exact answer: t->27.8973 Then you easily find that the rest of the solutions are (essentially, rounded to close rational): b /3; c (actually c .12 x 10^(-294)); o /3 Hope that helps. RF -----Original Message----- From: s2700114@nickel.laurentian.ca [SMTP:s2700114@nickel.laurentian.ca] To: mathgroup@smc.vnet.net Sent: Friday, January 30, 1998 3:25 AM To: mathgroup@smc.vnet.net Subject: [mg10698] weird eqns I have four equations ond would like mathematica to solve them using NSolve. everytime i try this it returns with a transcendental function error. I would like to solve thiese equations without have to manipulate them by hand. anybody with any ideas would be welcomed, Please email me as my newserver is spotty at best. Thanks Troy s2700114@nickel.laurentian.ca eone og[10, c] Ð(-38530+ 36*t)/(1.987*2.303*t); etwo Log[10, b] + 0.5*Log[10, o] - Log[10, c] Ð(-23000+2167*t)/(1.987*2.303*t); ethree + c + o Ð1; efour /o Ð0.5;

**nasty integrals that Mathematica can't do**

**Calc formula from table**

**Re: nasty integrals that Mathematica can't do**

**Calc formula from table**