Let $\alpha$ and $B$ be the roots of equation $x^2-6x-2=0$ .If $a_n= \alpha^n- \beta^n,$ for $n \geq 1$then the value of $ \large\frac{a_{10}-2_{a8}} {2a_{9}}$ is equal to :

Question

$\begin{array}{1 1} -3 \\ 6 \\ -6 \\ 3 \end{array} $