1.x+x^2-y-y^22.因式分解：x^2-y^2+2x-2y=?x^2 y+2xy+y-y^3=?3.计算：99.

1.x+x^2-y-y^2
＝(x-y)+(x^2-y^2)
= (x-y)+(x+y)(x-y)
=(x-y)(1+x+y)
2.因式分
x^2-y^2+2x-2y
= (x+y)(x-y)+2(x-y)
=(x-y)(x+y+2)
x^2 y+2xy+y-y^3
=y(x^2+2x+1-y^2)
=y[(x+1)^2-y^2]
=y(x+1+y)(x+1-y)
3.计算：99.9^2-0.1^2
=(99.9+0.1)(99.9-0.1)
=100×99.8
＝9980

4.因式分
x^2-4y^2-x+2y
＝（x+2y）(x-2y)-(x-2y)
=(x-2y)(x+2y-1）
(x^2+x)^2-8(x^2+x)+12
=(x^2+x-2)(x^2+x-6)
=(x+2)(x-1)(x+3)(x-2)