\(9\left(a-b\right)^2-4\left(x-y\right)^2\)
\(=\left[3\left(a-b\right)\right]^2-\left[2\left(x-y\right)\right]^2\)
\(=\left(3a-3b-2x+2y\right)\left(3a-3b+2x-2y\right)\)
\(=\left(3a-3b\right)^2-\left(2x-2y\right)^2\)
\(=\left(3a-3b-2x+2y\right)\left(3a-3b+2x-2y\right)\)