Express 1/r(r+1) in partial fractions and use the result to find the sum of the following series as a single fraction in terms of n:

1/1x2 + 1/2x3 + 1/3x2 + ............... + 1/n(n+1)

I can express it as partial fractions to 1/r - 1/r-1 but from there, I don't know, I don't think it's an arithmetic sequence as there is no common difference.

Thanks in advance.