I shall create a series of short expository articles with title “Why is …”, in order to illustrate some tiny but interesting questions in mathematics (more specifically, in calculus).
This is the first post.
Why is 
?
Well, let us consider the limit 
Taking logarithm, we can first evaluate the new limit 
Using L’Hôpital’s rule, we do it as follows. 
So the original limit is equal to 
Remark: One can also calculate the limit 
in the following way: we set 
, then we turn to evaluate the following limit: (Using L’Hôpital’s rule). 
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