若x\y=2\7,求7x^2-3xy+2y^2\2x^2-3xy+7y^2

xy=-2,x+y=3,求代数式（4xy+12y)+[7x-(3xy+4y-x)] 已知x=3y,试求(x-y)^2+2xy-y^2/x^2+7xy+y^2 1、(-7x^y)(2x^y-3xy^3+xy) 2、((x-y)^6)/((y-x)^3)/(x-y) 已知xy^2=-2求xy（2x^3y^7+5x^2y 已知X/Y=2/7,求x^2-3XY+2Y^2/X^2-2XY+Y^2 已知x/y=7/2,求2x+3xy+2y/x+2xy+y的值 已知1/x-1/y=2,求3x+7xy-3y/2x-3xy-2y 已知x+y=4,xy=2,求代数式2(3x+2xy)+(2xy+3x+2y)-(4xy-7y)的值 x+y=8,xy=-2,求(5xy+4x+7y)+(6x-3xy)-(4xy-3y)的值 若(y-x)/xy=3,求分式(2x+3xy-2y)/(x-2xy-y)的值 若y-x/xy=3,求分式2x+3xy-2y/x-2xy-y 若x+y-5xy=0,求(2x-3xy+2y)/(x+2xy+y)的值