已知:x-y=7,xy=5,则3xy-7x-7y=?

已知x-y=3xy,且xy不等于0,则-3x+6xy+3y/(7x-5y)-9xy-(3x-y) 已知xy^2=-2求xy（2x^3y^7+5x^2y 已知x+y=3,xy=1,求代数式5xy+4x+7y+6x-3xy-4xy+3y的值. 已知X+Y=6,xy=3求代数式（5XY+4X+7Y)+(6X-3XY)-(4XY-3Y)的值 已知x-y=5，xy=3，则3xy-7x+7y=______． 已知x=3y,试求(x-y)^2+2xy-y^2/x^2+7xy+y^2 已知xy^2=-3,求-xy(x^3y^7-3x^2y^5-y)的值 已知xy^2=-2求xy（2x^3y^7+5x^2y^5-y)的值 已知xy^2=-6,求-xy(x^3y^7-3x^2y^5-y）的值 已知xy^2=-2,求-xy(x^3y^7-3x^2y^5-y)的值 已知xy²=-6,求xy(x^3y^7-3x^2y^5-11.5y)的值 已知x+y=2xy,且xy不等于0,则求-2x+6xy-2y/(7x+5y)-9xy-(3x+y)=___