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 Caicedo, Wolfgang, quid Dec 24 '15 at 17:40
This question appears to be off-topic. The users who voted to close gave this specific reason: