几道因式分解```

十字相乘法：1、a²-2ab+b²-2a+2b+1

2、a²+4ab+4b²-2a-4b-3

3、如果分解x²-x+m得到两个因式（x+2）与（x-n）的积，求m+n的值.

分组分解法：1、a²-b²-2b-1

2、2x³-2x²y+8y-8x

3、（y+2）x²+（y+2）x-12y-24

4、x²-2x-y²-2y

5、8a²-8ab+2b²-32c²

1、a²-2ab+b²-2a+2b+1

=(a-b)²-2(a-b)+1

=(a-b+1)²

2、a²+4ab+4b²-2a-4b-3

=(a+2b)²-2(a+2b)-3

=(a+2b+1)(a+2b-3)

3、如果分解x²-x+m得到两个因式（x+2）与（x-n）的积

则2-n=-1 n=3 因为-2n=m,所以m=-6

分组分解法：1、a²-b²-2b-1

=a²-(b²+2b+1)

=a²-(b-1)²

=(a+b-1)(a-b+1)

2、2x³-2x²y+8y-8x

=2x²(x-y)-8(x-y)

=(2x²-8)(x-y)

=2(x²-4)(x-y)

=2(x+2)(x-2)(x-y)

3、（y+2）x²+（y+2）x-12y-24

=（y+2）x²+（y+2）x-12(y+2)

=(y+2)(x²+x-12)

=(x-3)(x+4)(y+2)

4、x²-2x-y²-2y

=x²-2x+1-y²-2y-1

=x²-2x+1-(y²+2y+1)

=(x-1)²-(y+1)²

=(x+y)(x-y-2)

5、8a²-8ab+2b²-32c²

=2(4a²-4ab+b²-16c²)

=2[(2a-b)²-(4c)²]

=2(2a-b+4c)(2a-b-4c)

1. (a+b)2-2(a+b)+1

=(a+b+1)2

2.(a+2b)2-2(a+2b)-3

=(a+2b+1)(a+2b-1)

3.(x+2)(x-n)

=x2-xn+2x-2n

=x2-(n-2)x-2n

所以-x=n-2,-2n=m

所以m+n=-4-3x

1.a2-(b+1)2

=(a-b-1)(a+b+1)

2.2(x3-x2y+y-x)

=2[x2(x-y)-(x-y)]

=2(x+1)(x-1)(x-y)

3.(y+2)(x2+x-12)

=(y+2)(x-3)(x+4)

4.(x+y)(x-y)-2(x+y)

=(x-y-2)(x+y)

5.2(4a)

如果分解x²-x+m得到两个因式（x+2）与（x-n）的积，求m+n的值

M=-6 N=3