O.k. I posted earlier concerning this question. I think I know have a better understanding of what's going on. Particle in a box with boundaries at x=L and x=3L. U(x) = A cos kx + B sin kx Applying boundary conditions, I get that 0 = A cos kL + B sin kL and that 0 = A cos 3kL + B sin 3kL How do I find A and B as well as the k values? Please help! Then I normalize U(x). I also had a question concerning the ground state wave function. In my first post, I was informed the ground state was a sine function for the situation x=0 to x=L. So for the case of x=L to x=3L, it should be a linear combination of sine and cosine. So is psi(x,0) = A cos kx + B cos kx? If not, then what? I really thought I understood the problem for x=0 to x=L, but the x=L to x=3L situation is giving me fits! Thanks for the help!