Why doesn't the sampling theorem work in this case? In this example, under &quot;Discussion&quot;, we can see that the Nyquist sample rate will result in samples with the value zero only. But why is this? I thought the sampling theorem said that if you sample with the Nyquist sample rate or higher, then the original signal can be exactly recovered? But in this case it can't? So does that mean the sample theorem is not actually valid?
The formula given is

$$ F_s &gt; 2F_{\mathrm{max}}$$

not 

$$ F_s \ge 2F_{\mathrm{max}}$$

otherwise it is possible that you could be sampling exactly on the zero crossing points. In practice you would choose sometime a bit higher. For example, CD audio uses 44100 Hz to represent signals up to 20000 Hz.