How can I prove that there exists a subsequence of $\{\cos(nr)\}_{n=1}^\infty $, where $r \in \mathbb{Q}$, that converges pointwise on $\mathbb{Q}$ to a real valued function?
Any help would be appreciated!
How can I prove that there exists a subsequence of $\{\cos(nr)\}_{n=1}^\infty $, where $r \in \mathbb{Q}$, that converges pointwise on $\mathbb{Q}$ to a real valued function?
Any help would be appreciated!
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