1.a²-b²-2b-12.(a-b)²+4ab3.(x+y)²-4(x+y-1)

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1.a²-b²-2b-1
2.(a-b)²+4ab
3.(x+y)²-4(x+y-1)

1.a^2-b^2-2b-1
=a^2-(b^2+2b+1)
=a^2-(b+1)^2
=(a+b+1)(a-b-1)
2.(a-b)^2+4ab
=a^2-2ab+b^2+4ab
=a^2+2ab+b^2
=(a+b)^2
3.(x+y)^2-4(x+y-1)
=(x+y)^2-4(x+y)+4
=(x+y-2)^2