Are You on the Right Track with Separation of Variables for PDEs?

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Homework Help Overview

The discussion revolves around the application of separation of variables in solving partial differential equations (PDEs). The original poster presents their approach to a problem involving boundary conditions that suggest oscillatory solutions.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to separate variables and derives equations for T(t) and X(x), expressing uncertainty about the choice of λ and its implications for the solution form. Some participants suggest adjustments to the parameters used, while others provide guidance on solving the characteristic equation.

Discussion Status

The discussion is ongoing, with participants providing feedback on the original poster's approach. There is an exchange of ideas regarding the characteristic equation and the implications of the parameters involved, but no consensus has been reached on the next steps.

Contextual Notes

The original poster notes a specific boundary condition that influences their choice of λ, indicating a potential assumption about the nature of the solution. There is also mention of the form of the solution depending on the values of β, k, and λ, which remains under discussion.

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Homework Statement


This is the first problem of the two.

Homework Equations


The Attempt at a Solution



Using separation of variables, I end up with

T'(t)= -λKT(t) and X''(x)+(β/K)X'(x)/X(x)= -λ. At first I chose the negative lambda because I saw that U(0,t) and U(L,t) needed to oscillate and I was hoping to get a sin function. Now the characteristic equation for X is something like r^2 + (β/K)r +λ=0 and I am not sure if I am on the right track in solving for the function X(x).
 

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You're on the right path, but it helps to use 2 instead of λ.
 
thanks. I guess what I should have said is that I am stuck at this point.
 
Solve the characteristic equation for r. The solution has the form C1Exp(rx)+C2Exp(-rx).
This might become D1sin(r'x)+D2cos(r'x) depending on the sizes of β, k, and λ.
Edit:If r was imaginary, r' is a new constant that is real.
 

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