已知x+y=7,xy=12,求(x^2 + 3xy +2y^2) / (x^2 y+2xy^2) 的值
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已知x+y=7,xy=12,求(x^2 + 3xy +2y^2) / (x^2 y+2xy^2) 的值
只能用 分式的变式
只能用 分式的变式
![已知x+y=7,xy=12,求(x^2 + 3xy +2y^2) / (x^2 y+2xy^2) 的值](/uploads/image/z/1353351-39-1.jpg?t=%E5%B7%B2%E7%9F%A5x%2By%3D7%2Cxy%3D12%2C%E6%B1%82%28x%5E2+%2B+3xy+%2B2y%5E2%29+%2F+%28x%5E2+y%2B2xy%5E2%29+%E7%9A%84%E5%80%BC)
(x^2 + 3xy +2y^2) / (x^2 y+2xy^2)
=(x+2y)(x+y)/[xy(x+2y)]
=(x+y)/(xy)
将x+y=7,xy=12代入
(x+y)/(xy)
=7/12
=(x+2y)(x+y)/[xy(x+2y)]
=(x+y)/(xy)
将x+y=7,xy=12代入
(x+y)/(xy)
=7/12
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