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因式分解,9(x-y)²-y²,9a²-4(b+c)²,(x+y+z)²

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因式分解,9(x-y)²-y²,9a²-4(b+c)²,(x+y+z)²-(x-y-z)²,
9(x-y)²-y²,
=[3(x-y)]²-y²
=[3(x-y)+y][3(x-y)-y]
=(3x-2y)(3x-4y)
9a²-4(b+c)²,
=(3a)²-[2(b+c)]²
=[3a+2(b+c)][3a-2(b+c)]
=(3a+2b+2c)(3a-2b-2c)
(x+y+z)²-(x-y-z)²
=[(x+y+z)+(x-y-z)][(x+y+z)-(x-y-z)]
=2x(2y+2z)
=4x(y+z)