已知x^2+y^2=12,x+y=4,则xy=
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已知xy/x+y=1/2,则代数式3x-5xy+3y/-x+3xy-y=
已知x-y=4xy,求x-2xy-y分之2x+3xy-2y的值!
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已知:x-y=1,xy=-2.求:(-2xy+2x+3y)-(3xy+2y-2x)-(x+4y+xy)的值
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已知x-y=3,xy=1,求(-2x+2x+3y)-(3xy+2y-2x)-(x+4y+xy)