Part A
Basically, since all of the examples are the same i chose a random person and that random person was Nicholas Block and he had cos(2t).
x[n]=cos(2n) is not periodic because there needs to be a factor of 2pi and since n is an integer, there is not going to be a period.
x(t)=cos(2t) is periodic everytime t has a factor of pi.
Part B
Cos[n] is periodic in discrete time when it is sampled in intervals of 2pi. It satisfies the equation: a[n+T]=a[n] for an integer T.
