设A=2x²-3xy+y²-x+2y,B=4x²-6xy+2y²+3x-y.若x
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设A=2x²-3xy+y²-x+2y,B=4x²-6xy+2y²+3x-y.若x-2a的绝对值+(y+3)²=0,且B-2A
求A的值
求A的值
∣x-2a∣+(y+3)²=0
因为∣x-2a∣≥0,(y+3)²≥0
所以∣x-2a∣=0,(y+3)²=0
所以x=2a,y=-3
B-2A=(4x²-6xy+2y²-3x-y)-2(2x²-3xy+y²-x+2y)
=4x²-6xy+2y²-3x-y-4x²+6xy-2y²+2x-4y
=-x-5y
=-2a+15
因为∣x-2a∣≥0,(y+3)²≥0
所以∣x-2a∣=0,(y+3)²=0
所以x=2a,y=-3
B-2A=(4x²-6xy+2y²-3x-y)-2(2x²-3xy+y²-x+2y)
=4x²-6xy+2y²-3x-y-4x²+6xy-2y²+2x-4y
=-x-5y
=-2a+15
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