For α, β ∈ R and a natural number n, let A_r= |r, 1, n^2/2+α; 2 r, 2, n^2-β; 3 r-2, 3, (n(3 n-1))/2|. Then 2 A_10-A_8 is

For $\displaystyle \alpha, \beta \in \mathbb{R}$ and a natural number $\displaystyle n$, let $\displaystyle A_r=\left|\begin{array}{ccc}r & 1 & \frac{n^2}{2}+\alpha \\ 2 r & 2 & n^2-\beta \\ 3 r-2 & 3 & \frac{n(3 n-1)}{2}\end{array}\right|$. Then $\displaystyle 2 A_{10}-A_8$ is