Hi, Im using mathematica 9. I made some code: CDeb[n_, t_, thD_] = n*9*8.31 (t/thD)^3 Integrate[ x^4 Exp[x]*(Exp[x] - 1)^-2, {x, 0, thD/t}]; CEl[t_, gamma_] = gamma*t; Cp[n_, t_, thD_, gamma_] = CDeb[n, t, thD] + CEl[t, gamma]; n = 5; fitt = FindFit[pun, Cp[n, T, ThetaD, GammA], {{ThetaD, 330}, {Gam...