已知,A=3x2+3y2-5xy,B=2xy-3y2+4x2,求:
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已知,A=3x2+3y2-5xy,B=2xy-3y2+4x2,求:
(1) 2A-B;
(2)当x=3,y=−
(1) 2A-B;
(2)当x=3,y=−
1 |
3 |
![已知,A=3x2+3y2-5xy,B=2xy-3y2+4x2,求:](/uploads/image/z/7436605-13-5.jpg?t=%E5%B7%B2%E7%9F%A5%EF%BC%8CA%3D3x2%2B3y2-5xy%EF%BC%8CB%3D2xy-3y2%2B4x2%EF%BC%8C%E6%B1%82%EF%BC%9A)
(1)2A-B=2(3x2+3y2-5xy)-(2xy-3y2+4x2)
=6x2+6y2-10xy-2xy+3y2-4x2
=2x2+9y2-12xy;
(2)当x=3,y=−
1
3时,
2A-B=2x2+9y2-12xy=31.
=6x2+6y2-10xy-2xy+3y2-4x2
=2x2+9y2-12xy;
(2)当x=3,y=−
1
3时,
2A-B=2x2+9y2-12xy=31.
已知,A=3x2+3y2-5xy,B=2xy-3y2+4x2,求:
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