
Aime F. answered 04/15/21
Experienced University Professor of Mathematics & Data Science
The given equation T''(x) = 0 has definite integrals T'(x) = T'(0) = T'(L), where L = 0.2m. The boundary conditions are kT'(0)=40000W/m2 and kT'(L)=25000W/m2, but these requirements are inconsistent with T'(0) = T'(L), so something seems to be mis-stated in your question. Also the "surface area" is of what surface? The univariate equation T''(x) = 0 doesn't imply a particular shape. Please check the problem statement, and if it is stated as given then provide its source and I will investigate.