Part 3 of a series of workbooks on sampling and aliasing. This workbook shows the result in the frequency domain of sampling a single 0.5Hz cosine signal. The reconstructed signal contains not onlyt he original cossine, but also aliases of the original signal at multiples of the sampling frequency plus and minus 0.5Hz. We can use a low pass reconstruction filter to eliminate the aliases as long as we sample fast enough that the nearest alias does not fold into or below the frequency of the original signal.