求x²-2xy+y²-9的值

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求x²-2xy+y²-9的值

x²-2xy+y²-9
=(x-y)²-9
=(x-y+3)(x-y-3)

x²-2xy+y²-9
=(x-y)^2-9
=(x-y+3)(x-y-3)

x²-2xy+y²-9
=(x+y)²-3²
=(x+y-3)(x+y+3)