已知A=3x2-4xy+2y2,B=x2+2xy-5y2.(1)求A+B;(2)求A-B;(3)若2A-B+C=0,求C
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(1)∵A=3x2-4xy+2y2,B=x2+2xy-5y2,
∴A+B=(3x2-4xy+2y2)+(x2+2xy-5y2)=3x2-4xy+2y2+x2+2xy-5y2=4x2-2xy-3y2;
(2)肆改饥∵A=3x2-4xy+2y2,B=x2+2xy-5y2,
∴A-B=(3x2-4xy+2y2)裂返-(x2+2xy-5y2)=3x2-4xy+2y2-x2-2xy+5y2=2x2-6xy+7y2;
(3)∵歼戚2A-B+C=0,
∴C=B-2A=(x2+2xy-5y2)-2(3x2-4xy+2y2)=x2+2xy-5y2-6x2+8xy-4y2=-5x2+10xy-9y2
∴A+B=(3x2-4xy+2y2)+(x2+2xy-5y2)=3x2-4xy+2y2+x2+2xy-5y2=4x2-2xy-3y2;
(2)肆改饥∵A=3x2-4xy+2y2,B=x2+2xy-5y2,
∴A-B=(3x2-4xy+2y2)裂返-(x2+2xy-5y2)=3x2-4xy+2y2-x2-2xy+5y2=2x2-6xy+7y2;
(3)∵歼戚2A-B+C=0,
∴C=B-2A=(x2+2xy-5y2)-2(3x2-4xy+2y2)=x2+2xy-5y2-6x2+8xy-4y2=-5x2+10xy-9y2
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A = 3x² - 4xy + 2y²,B = x² + 2xy - 5y²,运答猜
A + B = (3x² - 4xy + 2y²) + (x² + 2xy - 5y²举闷) = 4x² - 2xy - 3y²
A - B = (3x² - 4xy + 2y²) - (x² + 2xy - 5y²) = 2x² - 6xy + 7y²
2A - B + C = 0
C = B - 2A = (x² + 2xy - 5y²) - 2(3x² - 4xy + 2y²) = -5x²旁型 + 10xy - 9y²
A + B = (3x² - 4xy + 2y²) + (x² + 2xy - 5y²举闷) = 4x² - 2xy - 3y²
A - B = (3x² - 4xy + 2y²) - (x² + 2xy - 5y²) = 2x² - 6xy + 7y²
2A - B + C = 0
C = B - 2A = (x² + 2xy - 5y²) - 2(3x² - 4xy + 2y²) = -5x²旁型 + 10xy - 9y²
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