各位高手帮帮忙 急~

1)
(x+1)(x+6)(x+2)(x+3)+x^2
=(x^2+6x+6+x)(x^2+6x+6-x)+x^2
=(x^2+6x+6)^2-x^2+x^2
=(x^2+6x+6)(x^2+6x+6)
2)
1999x^2-(1999^2-1)x-1999
=(1999x+1)(x-1999)
3)
(x+y-2xy)(x+y-2)+(xy-1)^2
=(x+y-xy-1-(xy-1))(x+y-xy-1+(xy-1))+(xy-1)^2
=(x+y-xy-1)^2-(xy-1)^2+(xy-1)^2
=((x-1)^2)*(1-y)^2
4)
(2x-3y)^3+(3x-2y)^3-125(x-y)^3
=(2x-3y+3x-2y)((2x-3y)^2+(2x-3y)(3x-2y)+(3x-2y)^2)-(5x-5y)^3
=(5x-5y)((4+6+9-25)x^2-(12+13+12-50)xy+(9+6+4-25)y^2)
=(5x-5y)(-6x^2+13xy-6y^2)
=(5y-5x)(3x-2)(2x-3)
5)
a^2(b-c)+b^2(c-a)+c^2(a-b)
=a^2(b-c)+bc(b-c)-a(b^2-c^2)
=(b-c)(a^2+bc-a(b+c))
=(b-c)(a-b)(a-c)
6)
x^2+xy-2y^2-x+7y-6
=(x^2-xy+2x)+(2xy-2y^2+4y)-(3x-3y+6)
=x(x-y+2)+2y(x-y+2)-3(x-y+2)
=(x-y+2)(x+2y-3)