Substitute and simplify (if you know the limit holds for positive and negative n).
For your solution
Now use the substitution
This question seems like it should be so easy, but I just can't quite get there:
Use the fact that to deduce that .
So far this is what I have but I have a feeling i'm going about it the wrong way:
By algebra of limits:
So .
But from here I can't see how I can get the answer required.