Matrices And Determinants

Let $$A=\left[\begin{array}{ccc}-2 & x & 1 \\ x & 1 & 1 \\ 2 & 3 & -1\end{array}\right]$$. If the roots of the equation \(\operatorname{det} A=0\) are \(l, m\) then \(l^3-m^3=\)