已知A=3x²+3y²-5xy,B=2xy-3y²+4x²﹙1﹚求2A-B ﹙2﹚当x=3,y=-⅓时,求2A-B的值
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![已知A=3x²+3y²-5xy,B=2xy-3y²+4x²﹙1﹚求2A-B ﹙2﹚当x=3,y=-⅓时,求2A-B的值](/uploads/image/z/1999129-49-9.jpg?t=%E5%B7%B2%E7%9F%A5A%EF%BC%9D3x%26%23178%3B%2B3y%26%23178%3B%EF%BC%8D5xy%2CB%EF%BC%9D2xy%EF%BC%8D3y%26%23178%3B%2B4x%26%23178%3B%EF%B9%991%EF%B9%9A%E6%B1%822A%EF%BC%8DB+%EF%B9%992%EF%B9%9A%E5%BD%93x%EF%BC%9D3%EF%BC%8Cy%EF%BC%9D%EF%BC%8D%26%238531%3B%E6%97%B6%EF%BC%8C%E6%B1%822A%EF%BC%8DB%E7%9A%84%E5%80%BC)
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已知A=3x²+3y²-5xy,B=2xy-3y²+4x²﹙1﹚求2A-B ﹙2﹚当x=3,y=-⅓时,求2A-B的值
已知A=3x²+3y²-5xy,B=2xy-3y²+4x²
﹙1﹚求2A-B ﹙2﹚当x=3,y=-⅓时,求2A-B的值
已知A=3x²+3y²-5xy,B=2xy-3y²+4x²﹙1﹚求2A-B ﹙2﹚当x=3,y=-⅓时,求2A-B的值
1)2A-B=2(3x²+3y²-5xy)-(2xy-3y²+4x²)
=6x²+6y²-10xy-2xy+3y²-4x²
=2x²+9y²-12xy
2)把x=3,y=-⅓代入上式
2A-B=2·3²+9·(-1/3)²-12·3·-1/3
=18+1+12
=31
2A-B=2(3x²+3y²-5xy)-(2xy-3y²+4x²)
=6x²+6y²-10xy-2xy+3y²-4x²
=2x²+9y²-12xy