在讲提取公因式一课时,张老师出了这样一道题目:把多项式3(x-y)3-(y-x)2分解因式?并请甲、乙两名同学在黑板上演算.甲演算的过程:3(x-y)3-(y-x)2-3(x-y)3+(x-y)2=(x-y)2[3(x-y)+1]=(x-y)2(3x-3y+1).乙演算的过程:3(x-y)3-(y-x)2=3(x-y)3-(x-y)2=(x-y)2(3x-3y).他们的计算正确吗?若错误,请你写出正确答案.
若要把多项式-12xy2(x+y)+18x2y(x+y)因式分解,则应提取的公因式为______.