Hint: use the identity and and a two-sided limit. What do you find?
We are given to evaluate:
The first thing I am looking for is a way to apply the well-known result:
Seeing the denominator has as a factor, this takes me to . So we now have:
Now, let's use the substitution and we have:
Now let's finish rewriting the expression so we can apply (1):
Applying (1), we are left with:
Now, do we have: