Question

分解因式x²-y²-3x-3y

Answer 1

x²-y²-3x-3y=x²-y²-3(x+y)
=(x+y)(x-y)-3(x+y)
=(x+y)[(x-y)-3]
=(x+y)(x-y-3)

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追问

=(x+y)(x-y)-3(x+y)
=(x+y)[(x-y)-3]
为什么后面的（x+y）不见了

追答

提公因式：
(x+y)(x-y)-3(x+y)
=(x+y)[(x-y)-3]

Answer 2

x²-y²好型-3x-3y
=(x²-y²洞袜晌纳锋)-(3x+3y)
=(x+y)(x-y)-3(x+y)
=(x+y)[(x-y)-3]
=(x+y)(x-y-3)

Answer 3

原式=(x+y)(x-y)-3(x+y)
=(x+y)(x-y-3)