So if , then overestimates the value of and underestimates the value of
But that's not much of a proof.
I would like to prove the following inequalities,
1) , show that
2) Given that , prove that
It's in part of a book about power series expansion of functions, so I'm pretty sure they're looking for a solution involving those. I've put in the expansions for sin and cos but I don't see the logic in how to prove these statements for all x.
A nudge in the right direction would be much appreciated, thanks