解:(1)x(a+b)+y(a+b)=(a+b)(x+y).
(2)3a(x-y)-(x-y)=(x-y)(3a-1).
(3)6(p+q)²-12(q + p)=6(p+q)(p+q-2).
(4)a(m-2)+b(2-m)=a(m-2)=b(m-2)=(m-2)(a-b).
(5)2(y-x)²+3(x-y)=2(x-y)²+3(x-y)=(x-y)[2(x-y)+3]=(x-y)(2x-2y+3).
(6)mn(m-n)-m(n-m)²=mn(m-n)-m(m-n)²=m(m-n)[n-(m-n)]=m(m-n)(n-m+n)=m(m-n)(2n-m).