TITLE: Limit of definite sum equals $\ln(2)$
QUESTION [7 upvotes]: I have to show the following equality: 

$$\lim_{n\to\infty}\sum_{i=\frac{n}{2}}^{n}\frac{1}{i}=\log(2)$$

I've been playing with it for almost an hour, mainly with the taylor expansion of $\ln(2)$. It looks very similar to what I need, but it has an alternating sign which sits in my way.
Can anyone point me in the right direction?

REPLY [4 votes]: Truncate the Maclaurin series for $\log(1+x)$ at the $2m$-th term, and evaluate at $x=1$. Take for example $m=10$. We get 
$$1-\frac{1}{2}+\frac{1}{3}-\frac{1}{4}+\frac{1}{5}-\frac{1}{6}+\cdots+\frac{1}{19}-\frac{1}{20}.$$
Add $2\left(\frac{1}{2}+\frac{1}{4}+\frac{1}{6}+\cdots +\frac{1}{20}\right)$, and subtract the same thing, but this time noting that
$$ 2\left(\frac{1}{2}+\frac{1}{4}+\frac{1}{6}+\cdots +\frac{1}{20}\right)=1+\frac{1}{2}+\frac{1}{3}+\cdots+\frac{1}{10}.$$
We get
$$\left(1+\frac{1}{2}+\frac{1}{3}+\cdots+\frac{1}{10}+\frac{1}{11}+\cdots+\frac{1}{20}\right)-\left(1+\frac{1}{2}+\frac{1}{3}+\cdots+\frac{1}{10}\right).$$
There is nice cancellation, and we get
$$\frac{1}{11}+\frac{1}{12}+\cdots+\frac{1}{20}.$$