(3a-2b)^2-(3a-2b)(2a-3b)
＝9a^2-12ab+4b^2-6a^2+13ab-6b^2
=3a^2+ab-2b^2
2m(x-y)+3n(y-x)
= 2m(x-y)-3n(x-y)
=(2m-3n)(x-y)