how did it find this 1-1/(n+1) ?
if is subtract 1/n - 1/n+1 the result is different
Basically saying all the terms $\displaystyle \frac{1}{2}, \frac{1}{3}, ..., \frac{1}{n} $ terms get cancelled out leaving you with a 1 from backet 1, and $\displaystyle \frac{-1}{n+1}$ from bracket 2, so you get $\displaystyle 1 - \frac{1}{n+1} $