- (a) Express \(\frac { 2 } { r \left( r ^ { 2 } - 1 \right) }\) in partial fractions.
(b) Hence find, in terms of \(n\),
$$\sum _ { r = 2 } ^ { n } \frac { 1 } { r \left( r ^ { 2 } - 1 \right) }$$
Give your answer in the form
$$\frac { n ^ { 2 } + A n + B } { C n ( n + 1 ) }$$
where \(A\), \(B\) and \(C\) are constants to be found.