Let α and β be the roots of equation x^2-6 x-2=0. If a_n =α^n -β^n, for n ≥ 1, then the value of (a_10-2 a_8)/(2 a_9) is equal to:

Let $\displaystyle \alpha$ and $\displaystyle \beta$ be the roots of equation $\displaystyle x^2-6 x-2=0$. If $\displaystyle \mathrm{a}_{\mathrm{n}}=\alpha^{\mathrm{n}}-\beta^{\mathrm{n}}$, for $\displaystyle \mathrm{n} \geqslant 1$, then the value of $\displaystyle \frac{\mathrm{a}_{10}-2 \mathrm{a}_8}{2 \mathrm{a}_9}$ is equal to :