I encountered a problem today to prove that $\cos (n!)$ does not have a limit. I have no idea how to do it formally. Could someone help? The simpler the proof (by that I mean less complex theorems are used) the better.
closed as off-topic by Johannes Hahn, paul garrett, Andrés E. Caicedo, Wolfgang, user9072 Dec 24 '15 at 17:40
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