9-4x²+4xy-y²

9-4x²+4xy-y²
9-4x²+4xy-y²

9-4x²+4xy-y²
9-4x²+4xy-y²
=3²-(4x²-4xy+y²)
=3²-(2x-y)²
=(3-2x+y)(3+2x-y)
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9-4x²+4xy-y²
=9-（4x²-4xy+y²）
=3²-（2x-y）²
=[3+(2x-y)][3-(2x-y)]
=(3+2x-y)(3-2x+y)

9-4x^2+4xy-y^2=9-(2x+y)^2=(3+2x+y)(3-2x-y)