The function I chose (at random) from homework1 can be found here.
The function x(t) = cos(t) is periodic in CT, as its period is 2$ \pi $. However, it is not periodic in DT.
Here is the function sampled at a frequency of 5 samples/unit:
Here is the function sampled at $ {\pi \over 2} $ (as closely as MATLAB is able to approximate pi)