I've to prove that as we take the limit of cosine as x goes to + infinity, the limit DNE. I've looked on different forums and sites, but all have methods I barely understand. I'm not very familiar with the Delta-Epsilon definition of limits. I've tried to look at the sticky at the top and try to understand but this is due tomorrow and I won't learn it at the moment unless it's the only way.
What's a good way to start off a proof like this? I know the reasons why it doesn't exist, as it oscillates between -1 and 1, but I need to have a proof.