9231 P12 - Nov 2013 - Q3 - 7 marks
6421
It is given that
\(S_{n}=\sum_{r=1}^{n} u_{r}=2 n^{2}+n\)
Write down the values of \(S_{1}, S_{2}, S_{3}, S_{4}\). Express \(u_{r}\) in terms of \(r\), justifying your answer.
Find
\(\sum_{r=n+1}^{2 n} u_{r} .\)
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