3. (a) Express \(\frac { 2 } { ( r + 1 ) ( r + 3 ) }\) in partial fractions.
(b) Hence show that $$\sum _ { r = 1 } ^ { n } \frac { 2 } { ( r + 1 ) ( r + 3 ) } = \frac { n ( 5 n + 13 ) } { 6 ( n + 2 ) ( n + 3 ) }$$ (c) Evaluate \(\sum _ { r = 10 } ^ { 100 } \frac { 2 } { ( r + 1 ) ( r + 3 ) }\), giving your answer to 3 significant figures.