已知A=4x2-4xy+y2,B=x2+xy-5y2,求A-3B.
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已知A=4x2-4xy+y2,B=x2+xy-5y2,求A-3B.
![已知A=4x2-4xy+y2,B=x2+xy-5y2,求A-3B.](/uploads/image/z/18537138-18-8.jpg?t=%E5%B7%B2%E7%9F%A5A%3D4x2-4xy%2By2%EF%BC%8CB%3Dx2%2Bxy-5y2%EF%BC%8C%E6%B1%82A-3B%EF%BC%8E)
∵A=4x2-4xy+y2,B=x2+xy-5y2,
A-3B=4x2-4xy+y2-3(x2+xy-5y2),
=4x2-4xy+y2-3x2-3xy+15y2,
=x2-7xy+16y2.
A-3B=4x2-4xy+y2-3(x2+xy-5y2),
=4x2-4xy+y2-3x2-3xy+15y2,
=x2-7xy+16y2.
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