1. The problem statement, all variables and given/known data Need to find the probability density of a ground state in an infinite square well. 2. Relevant equations Ground State psi(x) = Asin(Bx), don't want to look up the constants, don't think they are relevant anyway. 3. The attempt at a solution Took the derivative of psi(x) with respect to x to get momentum, times h/(2*pi*i). Then tried to integrate psi*psi, but before I did that I stopped myself, because taking the limits of integration to be infinity and negative infinity like for the position probability, I'd end up with 0. Since I get cos(x)^2 = 1 - sin(x)^2 Sin(x)^2 integrated from -inf. to inf. = 1, so this would be 0. That doesn't make sense, so it's clearly not the way to go about it. Should I go a step deeper and just try to solve Schrodinger's equation for momentum? Would that mean I have to take d/dx for the whole thing and then solve it? This problem is harder than I thought it would be.