若3x²-4xy+y²=-3,2x²+3xy-2y²=8,求5x²-18xy+7y²的值
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![若3x²-4xy+y²=-3,2x²+3xy-2y²=8,求5x²-18xy+7y²的值](/uploads/image/z/975770-26-0.jpg?t=%E8%8B%A53x%26%23178%3B-4xy%2By%26%23178%3B%3D-3%2C2x%26%23178%3B%2B3xy-2y%26%23178%3B%3D8%2C%E6%B1%825x%26%23178%3B-18xy%2B7y%26%23178%3B%E7%9A%84%E5%80%BC)
若3x²-4xy+y²=-3,2x²+3xy-2y²=8,求5x²-18xy+7y²的值
若3x²-4xy+y²=-3,2x²+3xy-2y²=8,求5x²-18xy+7y²的值
若3x²-4xy+y²=-3,2x²+3xy-2y²=8,求5x²-18xy+7y²的值
3x²-4xy+y²=-3 左右两边都乘以3,可以得到9x²-12xy+3y²=-9(1)
2x²+3xy-2y²=8 左右两边都乘以2,可以得到4x²+6xy-4y²=16(2)
(1)-(2)可以得到 5x²-18xy+7y²=-25
①3x²-4xy+y²=-3
②2x²+3xy-2y²=8
①x3得:9x²-12xy+3y²=-9③
②x2得:4x²+6xy-4y²=16④
③-④得:5x²-18xy+7y²=-25