1、原式=(7+x)(a-1)
2、原式=3(a-b)方-6(a-b)=3(a-b)(a-b-2)
3、原式=(m-n)(2m-2n-m)=(m-n)(m-2n)
4、原式=x(x-y)方-y(x-y)方=(x-y)(x-y)方=(x-y)立方
5、原式=(m+n)(a方+b方)
6、原式=18(a-b)立方-12b(a-b)方=6(a-b)方(3a-3b-2b)=6(a-b)方(3a-5b)
7、原式=(2a+b)(2a-3b-3a)= -(2a+b)(a+3b)
8、原式=(x+y)(x方-xy-x方-xy)=(x+y)(-2xy)= -2xy(x+y)