因式分解~求救

1.) 6x - 6y - 9x^2 + 18xy - 9y^2 - 1
= 6(x - y) - 9(x^2 - 2xy + y2) - 1
= 6(x - y) - 9(x - y)^2 - 1
Let x - y = u
6u - 9u2 - 1
= -(9u2 - 6u + 1)
= -(3u - 1)^2
= -[3(x - y) - 1]^2
= -(3x - 3y - 1)^2
2.) 1 + a + b + c + ab + bc + ac + abc
= 1 + b + c + bc + a + ab + ac + abc
= (1 + b + c + bc) + a(1 + b + c + bc)
= (1 + a)[(1 + b) + c(1 + b)]
= (1 + a)(1 + b)(1 + c)
3.) a^3(a - 2b) - b^3(b - 2a)
= a^4 - 2a^3b + 2ab^3 - b^4
= a^4 - b^4 - 2a^3b + 2ab^3
= (a^2 + b^2)(a^2 - b^2) - 2ab(a^2 - b^2)
= (a^2 - 2ab - b^2)(a^2 - b^2)
= (a - b)^2(a + b)(a - b)
= (a + b)(a - b)^3
4.) (1+x)^4 - (1 - x^2)^2
= [(1 + x)^2]^2 - (1 - x^2)^2
= [(1 + x)^2 + (1 - x^2)][(1 + x)^2 - (1 - x^2)]
= [1 + 2x + x^2 + 1 - x^2][1 + 2x + x^2 - 1 + x^2]
= [2 + 2x][2x + 2x^2]
= 4x(1 + x)^2
5.) a^2b + ab^2
= ab(a + b)
6.) a^2b + ab^2 + 7a + 7b
= ab(a + b) + 7(a + b)
= (ab + 7)(a + b)