1. The problem statement, all variables and given/known data (infinity)sigma(n=4) [ (2 / n) - (2 / (n -1)) ] 2. Relevant equations Harmonic series and ratio? 3. The attempt at a solution It's supposed to converge to -2/3, but, I don't know how. The first compare to a harmonic series and we see that goes to 0. The second, we use a ratio test or something and then compare it? If we simply take the limit it goes to 0. I don't know how to show it.