$ (2) \sum^{\infty}_{n=-\infty} \delta(t-nT) -> \frac{2\pi}{T}\sum^{\infty}_{k=-\infty}\delta(w-\frac{2\pi k}{T})\, $. . . . . . . . . . . . . . . . . . . . . . ., $ a_{k}=\frac{1}{T} $ for all k
