First off, this is not a homework problem. I was reading Charles Kittel solid states book on Chapter 2, equation 3:
electron number density, n(x), expanded in a Fourier series:
n(x) = n_0 + \sum_{p} [C_p cos(\frac{2\pi p x}{a}) + S_p sin(\frac{2\pi p x}{a})]
From this expansion, wouldn't...