1.(x-3)^2＋（3x-9）
=(x-3)^2+3(x-3)
=(x-3)(x-3+3)
=x(x-3)
2.x^2(a+b)-a-b
=x^2(a+b)-(a+b)
=(a+b)(x^2-1)
=(a+b)(x+1)(x-1)
3.2a(x-2y)^2-3b(2y-x)^3-4c(2y-x)^4
=2a(x-2y)^2+3b(x-2y)^3-4c(x-2y)^4
=(x-2y)^2[2a+3b(x-2y)-4c(x-2y)^2]
=(x-2y)(2a+3bx-6by-4cx^2+16cxy-16cy^2)
4.ab+cd+bc+ad
=(ab+ad)+(cd+bc)
=a(b+d)+c(b+d)
=(a+c)(b+d)
5.x^4－x^3＋3x-3
=x^3(x-1)+3(x-1)
=(x-1)(x^3+3)
6.a^2-a+b-b^2
=(a^2-b^2)-(a-b)
=(a-b)(a+b)-(a-b)
=(a-b)(a+b+1)