2021 SJI P1 Q2

The sum of the first \(n\) terms of a sequence is

\[\sum_{r=1}^n u_r=n^2+n-1,\]

for \(n\in\mathbb Z^+\).

1. 1. Find \(u_1\).
   2. Find an expression for \(u_n\) in terms of \(n\) for any positive integer \(n\geq2\).[4]
2. Hence, state with reason whether the sequence is arithmetic or not.[2]