Ok, so I am a little unsure of how to apply these new concepts I am learning. Here is a question. The function g(x)=x(x-a)e^ikx is in a certain Hilbert space where the finite norm squared equals the integral of the product of Psi's complex conjugate and Psi (dx) is less than infinity. I must calculate the coefficients of expansion (an) of this function in the series Psi(x)=summation of n=1 to infinity of (an*(Psi n(x))) where Psi n is the set of basis functions Psi n=(sqrt(2/a))sin(n*pi*x/a) I am not sure how to do this exactly. If I am unclear, please do tell me and I shall write some more. Peace, and thanks a lot dudes. Oh by the way, here Psi(x)=g(x) if that wasn't made obvious.