求代数式 2x^+(-x^+3xy+2y^)-2(x^-xy+2y^) 的值 其中 (2x-1)^+丨y+1丨=0
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求代数式 2x^+(-x^+3xy+2y^)-2(x^-xy+2y^) 的值 其中 (2x-1)^+丨y+1丨=0
![求代数式 2x^+(-x^+3xy+2y^)-2(x^-xy+2y^) 的值 其中 (2x-1)^+丨y+1丨=0](/uploads/image/z/16520423-23-3.jpg?t=%E6%B1%82%E4%BB%A3%E6%95%B0%E5%BC%8F+2x%5E%2B%EF%BC%88-x%5E%2B3xy%2B2y%5E%EF%BC%89-2%EF%BC%88x%5E-xy%2B2y%5E%29+%E7%9A%84%E5%80%BC+%E5%85%B6%E4%B8%AD+%282x-1%29%5E%2B%E4%B8%A8y%2B1%E4%B8%A8%3D0)
(2x-1)^2>=0,丨y+1丨>=0
(2x-1)^2+丨y+1丨=0
所以(2x-1)^2=0,丨y+1丨=0
得x=1/2,y=-1
2x^2+(-x^2+3xy+2y^2)-2(x^2-xy+2y^2)
=2x^2-x^2+3xy+2y^2-2x^2+2xy-4y^2
=-x^2+5xy-2y^2
=-(1/2)^2+5(1/2)(-1)-2(-1)^2
=-17/4
(2x-1)^2+丨y+1丨=0
所以(2x-1)^2=0,丨y+1丨=0
得x=1/2,y=-1
2x^2+(-x^2+3xy+2y^2)-2(x^2-xy+2y^2)
=2x^2-x^2+3xy+2y^2-2x^2+2xy-4y^2
=-x^2+5xy-2y^2
=-(1/2)^2+5(1/2)(-1)-2(-1)^2
=-17/4
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