[tex]\begin{gathered} \text{Function = (n + 1)}^2\text{ - 1} \\ \\ \text{where n }\ge\text{ 2} \end{gathered}[/tex]
[tex]\begin{gathered} (n+1)^2\text{ - 1} \\ (n\text{ + 1)(n + 1) - 1} \\ n^2\text{ + n + n + 1 - 1} \\ \text{Function = n}^2\text{ + 2n} \end{gathered}[/tex]
Final answer
[tex]\text{The function n}^2\text{ + 2n is a quadratic function.}[/tex]