The Hydrogen Atom wave function. With the substitution u(r) = r.R(r) p=kr We get a simplified version: d^2u/dp^2 = [1 - (p_0)/p + l(l + 1)/(p^2) ].u Im sure some of you have seen that before. Now, in the limit, p goes to infinity, I understand that we get u = A.exp[-p], but in the limit that p goes to 0, the answer is: d^2u/dp^2 = [l(l + 1)/(p^2)].u I dont get where that comes from. Surely the terms with p at the bottom explode and become infinite??