Problem solving equation
- To: mathgroup at smc.vnet.net
- Subject: [mg40741] Problem solving equation
- From: heathdwatts at hotmail.com (Heath)
- Date: Tue, 15 Apr 2003 04:01:03 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Hi, 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 Where am I making an error? Is my hand calculation wrong, or is Mathematica wrong? Why am I getting an error message using Solve[] or NSolve[] with Mathematica? Thanks, Heath