已知|x|=3,|y|=7,而xy

已知|x|=3,|y|=7,而xy 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=3y,试求(x-y)^2+2xy-y^2/x^2+7xy+y^2 已知x-y=4xy，则2x+3xy-2yx-2xy-y 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=4,xy=2,求代数式2(3x+2xy)+(2xy+3x+2y)-(4xy-7y)的值 已知1/x-1/y=2,求3x+7xy-3y/2x-3xy-2y 已知x/y=7/2,求2x+3xy+2y/x+2xy+y的值 已知X/Y=2/7,求x^2-3XY+2Y^2/X^2-2XY+Y^2 由已知x+y=-2,xy=3那么2(x+xy)-[(xy-3y)-x]-(-xy)等于多少?