Sampling Theorem
(Test question to state in your own words!)
Let $ \omega_m $ be a non-negative number.
Let x(t) be a signal with $ X(\omega)=0 $ when $ |\omega|>\omega_m $ (ie a band limited signal)
Consider the samples x(nT), for n=0, 1, -1, 2, -2, ...
If
$ T<\frac{1}{2}(\frac{2\pi}{\omega_m}) $
then x(t) can be uniquely recovered from its samples.
