1、(a+b)^4-(a+b)^2=＜（a+b)^ 2+a+b)＞＜（a+b)^2-a-b＞=(a+b)(a+b+1)＜（a+b)^2-a-b＞2、x^2(x-y)+y^2(x-y)=(x-y)(x^2-y^2)=(x-y)(x+y)(x-y)=(x+y)(x-y)^23、(7m+3n)^2-(5m+7n)^2=(7m+3n+5m+7n)(7m+3n-5m-7n)=(12m...确定对？确定