1. The problem statement, all variables and given/known data Please take a look at: http://www-solar.mcs.st-and.ac.uk/~alan/MT2003/PDE/node21.html Look at step 2.53. Can you explain to me how c^2*T'/T = k becomes T' = k*T*c^2? 3. The attempt at a solution I don't get it. What am I missing here?