$$\left. \begin{array} { l } { 6 , 12 } \\ { a ^ { 2 } - b ^ { 2 } , a - b } \\ { ( x + y ) ^ { 2 } , x ^ { 2 } - x y - 2 y ^ { 2 } } \end{array} \right.$$
$12\left(x-2y\right)\left(x+y\right)^{2}\left(a^{2}-b^{2}\right)$
$6,\ 12,\ a^{2}-b^{2},\ a-b,\ \left(x+y\right)^{2},\ \left(x-2y\right)\left(x+y\right)$
