9(x+2y)²-25（x-2y)²=

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9(x+2y)²-25（x-2y)²=
9(x+2y)²-25（x-2y)²=

9(x+2y)²-25（x-2y)²=
9(x+2y)^2-25(x-2y)^2
=[3(x+2y)+5(x-2y)][(3(x+2y)-5(x-2y)]
=(8x-4y)(-2x+16y)
=-8(2x-y)(x-8y)

9(x+2y)²-25（x-2y)²=9(x²+4xy+4y²)-25(x²-4xy+4y²)=-16x²+136xy-64y²