Question

x[n]=x[n+r]

Now, if x[n]=A*cos[w*n+B] is Discrete Time periodic signal, then prove that

w*r=2*pi*q, where q is integer.

Answer 1

Here's a clue: the solution hinges on the fact that:
\[\cos \theta=\cos(\theta \pm 2k \pi), k \in \mathbb{N}\]

Answer 2

thank you, CheesePi!

May Allah Ta'ala guide you and us.