\[\boxed{\text{642\ (642).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[ax - 2x = a^{3} - 2a^{2} - 9a + 18\]
\[x(a - 2) = a^{2}(a - 2) - 9(a - 2)\]
\[x(a - 2) = (a - 2)\left( a^{2} - 9 \right)\]
\[\ x = a^{2} - 9.\ \]