Given the matrix $$A = {\left[\begin{array}{ccc} a &2 &6\cr a &-8 &8\cr 9 &1 &a\cr \end{array}\right]}$$ find all values of $\displaystyle{a}$ that make $\displaystyle{ \lvert A \rvert = 0 }$. Give your answer as a comma-separated list. (The symbol $\displaystyle{ \lvert A \rvert }$ stands for the determinant of $\displaystyle{A}$.) Values of $\displaystyle{a}$: .