I've always pondered this question when it came to Fourier series and I think I've just proved it.
Let any even number be equal to 2k for all k in Z, then if k=0, 2k=0, an even number. Just what was to be shown.
Let any even number be equal to 2k for all k in Z, then if k=0, 2k=0, an even number. Just what was to be shown.