化简（a²-2ab)-(3a²+3ab)=( )

（a²-2ab)-(3a²+3ab)
=a²-2ab-3a²-3ab
=-2a²-5ab
=-a(2a+5b)
ab-a+b-1
=a(b-1)+(b-1)
=(a+1)(b-1)
2xy-x²-y²+1
=-(x²-2xy+y²)+1
=-(x-y)²+1
=-[(x-y)²-1]
=-(x-y+1)(x-y-1)