7(a-1)+x(a-1)=(7+x)(a-1)3(a-b)²+6(a-b)=(a-b)(3(a-b)+6)=(a-b)(3a-3b+6)2(m-n)²-m(m-n)=(m-n)(2(m-n)-m)=(m-n)(2m-2n-m)=(m-n)(m-2n)x(x-y)²-y(y-x)²=x(x-y)²-y(x-y)²=(x-y)²(...内个我还有几道需要解答一下18（a-b）³-12b（b-a）²，（2a+b）（2a-3B）-3a（2a+b）谢谢