Re: Problem solving equation
- To: mathgroup at smc.vnet.net
- Subject: [mg40761] Re: Problem solving equation
- From: dennisw555 at aol.com (DennisW555)
- Date: Wed, 16 Apr 2003 01:38:04 -0400 (EDT)
- References: <b7gfe0$eba$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
<< I'm trying to solve the following equation: Solve[1.046*Exp[.0151*t] + 1.284*Exp[.0087*t] == 6.3, t] and am getting this error message: Solve::"tdep": "The equations appear to involve the variables to be solved \ for in an essentially non-algebraic way." I cannot solve it with Solve[] or NSolve[]. I was able to find the solution by using Plot[] to get an idea where the solution is, followed by FindRoot[]. Why doesn't the expression simplify to, as I believe it does on paper, to: Log[1.046*Exp[.0151*t]] + Log[1.284*Exp[.0087*t]] == Log[6.3] Log[1.046]+Log[Exp[.0151*t]]+Log[1.284]+Log[Exp[.0087*t]]==Log[6.3] Log[1.046*1.284]+.0151*t+.0087*t==Log[6.3] .0238*t==Log[6.3]-Log[1.046*1.284] .0238*t==Log[6.3/(1.046*1.284)] .0238*t==1.545596 t==64.94 This "hand" solution is not the same as the solution I get using FindRoot[] in Mathematica. Mathematica finds the solution is: t==82.9182 >><BR><BR> Your hand calculation is wrong. The Log of a sum is not the sum of the logs. Dennis