1. The problem statement, all variables and given/known data This is a problem regarding transient heat conduction in an undefined semi-infinite solid, initially at a temperature T0 whose surface temperature is suddenly raised to a new constant level at Ts. I also supplied the problem as an attachment for ease in explaining the problem. We want to: Derive the Energy Equation State initial and boundary conditions Define two new variables η=Cxtm θ=(T-T0)/(Ts-T0) Determine C and m (the constants?) of η and θ from Part 3 Solve for η and θ themselves. I understand and completed Parts 1 and 2 of this problem. Unfortunately I dont understand how to begin Part 3... I assume its a method of Separation of Variables? 2. Relevant equations There are a decent amount of equations for transient heat conduction, but I dont think Parts 3, 4, and 5 relate to any specific equation. I think its a method (I forget the name) of where you define new equations so that you can re-define the variables, then plug into the original Energy equation (shown in Part 1). 3. The attempt at a solution Here is what I've tried so far. I am getting very lost on what variables to solve for, which ones to take derivatives of, etc... I would appreciate it if someone could help me get started if I'm wrong, or point me in the right direction if I am on the right track. Thanks in advance.