因式分解:25(x+y)²-9(x-y)²;(x+y)²-4(x+y-1).

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因式分解:25(x+y)²-9(x-y)²;(x+y)²-4(x+y-1).

25(x+y)²-9(x-y)²
=[5(x+y)-3(x-y)][5(x+y)+3(x-y)]
=(2x+8y)(8x+2y)
=4(x+4y)(4x+y)

(x+y)²-4(x+y-1).
=(x+y)²-4(x+y)+4
=(x+y-2)^2