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(2x-3)²-(x+y)(x-y)-y²
=4x²-12x+9-x²+y²-y²
=3x²-12x+9
=3x²-12x-3+12
=3(x²-4x-1)+12
=12
2、k²-4×9×4=0
k²=144
∴k=12或k=-12
=4x²-12x+9-x²+y²-y²
=3x²-12x+9
=3x²-12x-3+12
=3(x²-4x-1)+12
=12
2、k²-4×9×4=0
k²=144
∴k=12或k=-12
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