12x^2yz-9x^2y^2 -x^2+xy-xz p(x-y)+q(y-x)
=3x^2y·(4z)-3x^2y·(3y) =-x·x+(-x·-y)+(-x·z) =p(x-y)-q(x-y)
=3x^2y(4z-3y) =-x(x-y+z) =(p-q)(x-y)
2a(b-c)-3b(c-b) 6(2a+b)(2a-3b)-3(b+2a)
=2a(b+c)+3b(b-c) =3(b+2a)[2(2a-3b)-1]
=(b-c)(2a+3b) =3(b+2a)(4a-6b-1)
12a(x^2+y^2)-18b(x^ 2+y^2)
=(12a-18b)(x^ 2+y^2)