①3(a+b)²-27c²=3【(a+b)²-(3c)²】=3(a+b-3c)(a+b+3c)
②a²(a-b)+b²(b-a)=a²(a-b)-b²(a-b)=(a²-b²)(a-b)=(a-b)(a+b)(a-b)=(a-b)²(a+b)
③第三题你检查下 题目后面是不是3m²+5n²
(5m²+3n²)²-(3m²+5n²)²=(5m²+3n²-3m²-5n²)(5m²+3n²+3m²+5n²)=(2m²-2n²)(8m²+8n²)=16(m²-n²)(m²+n²)=16(m²+n²)(m+n)(m-n)
④(a²-b²)+(3a-3b)=(a+b)(a-b)+3(a-b)=(a-b)(a+b+3)