1. The problem statement, all variables and given/known data Find the expectation value of position as a function of time. 2. Relevant equations This is in the latter half of a multi-part question, previously we were given that: Eqn 1: Ψ(x, t) = A(ψ1(x)e−iE1t/h¯ + iψ2(x)e−iE2t/h¯) and in an even earlier part: Eqn 2: ψn(x) = sqrt(2/L)sin(n*pi*x/L) Note: h¯ = hbar 3. The attempt at a solution As you can tell, I'm not too awesome at formatting on here so I'm going to quickly explain my method. I said: <x> = Integral from 0 to L of Ψ*(x, t)Ψ(x, t) dx So I told wolframalpha (we're allowed to use it) to simplify Eqn 1, before subbing in Eqn 2. This gave me: Eqn 3: -2(ψ1ψ2sin(t(E1-E2)/h¯) + ψ12 + ψ22 I then subbed in Eqn 2 into Eqn 3 and integrated. No matter how many times I do this I always end up with a bunch of sines. These sines are all something like sin(n*pi/L) so when I sub in the limits of integration they become sin(n*pi) or sin(0), both of which are 0! This means that I'm just left with an answer of 2, which is not time dependent. Can anyone see where I've gone wrong?