1、(1)(x+y)·(x-y)
=x²-y²;
(2)a²-4a+4
=a(a-4)+4;
(3)m²n-8n
=n(m-8);
(4)x²+4x+2
=x²+2(2x+1)
2、解:(1)x² +xy
=x(x+y);
(2)-4b²+2ab
=-2b(2b-a);
(3) 3ax-12bx+3x
= 3x(a-4b+1);
(4)6ab³-2a² b²+4a³b
=2ab(3b²-ab+2a² ).
3、解:(1)2(x-y)-(x-y)²
=(x-y)(2-x+ y);
(2)6(m-n) ² +3 (m-n)-3(m-n)·[2 (m-n)+1]
=3(m-n)(2m- 2n+1).