I've come across Problem 2.2 out of Griffiths' Intro to Quantum book second edition. The problem says to show that E must exceed the minimum value of V(x) for all normalizable solutions to the Schroed. eq. Naturally I started with the normalization condition: int(|phi|^2)=1 and started taking derivatives on this. However, I cannot arrive at a contradiction. Any thoughts? Or any other ways to show the same result? Thanks.