9(x-y)^2-4(x+y)^2

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9(x-y)^2-4(x+y)^2
9(x-y)^2-4(x+y)^2

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