# Fourier Series Tolstov Book Question

by Chacabucogod
Tags: book, fourier, series, tolstov
 P: 42 I'm currently reading Tolstov's Fourier series and in page 58 he talks about a criterion for the completeness of a system. I've attached the pages where he talks about it. In general, I don't get how he came up with this; specifically, why does he use those limits of $\epsilon$ and $\epsilon$/4? -Thank you Attached Thumbnails