（1）2a三次方-2a²b+8b-8a （2）3a三次方-3ab²-21a²-21ab （3）-81-8ab+a²+16b²

1、=2a²(a-b)-8(a-b)=2(a-b)(a²-4)=2(a-b)(a+2)(a-2)2、=3a(a²-b²)-21a(a+b)=3a(a+b)(a-b)-21a(a+b)=3a(a+b)(a-b-7)3、=a²-8ab+(4b)²-81=(a-4b)²-9²=(a-4b+9)(a-4b-9)4、=...