X-2Y=1 x^2-xy-2y^2=7 联立

化简求值x-4y/2x-7xy+3y×x-2xy-3y/2x+3xy-2y÷3x-6y/4x-4xy+y,其中：x=1999,y=-1 若1/x-1/y=2,求3x-2xy-3y/x-xy-y的值3x-2xy-3y/x-xy-y 不好意思，是3x-2xy-3y/x-2xy-y 6（x-y)-7(xy)=21,2(x-y)-5(x+y)=-1 已知1/x-1/y=2,求3x+7xy-3y/2x-3xy-2y答案是1/x-1/y=2(y-x)/xy=2 得：x-y=-2xy(3x+7xy-3y)/(2x-3xy-2y)=[3(x-y)+7xy]/[2(x-y)-3xy]=(-6xy+7xy)/(-4xy-3xy)=xy/(-7xy)=-1/7 谁能帮我解释一下=[3(x-y)+7xy]/[2(x-y)-3xy]=(-6xy+7xy)/(-4xy-3xy) 是怎 已知x+y=-1,xy=-2,求代数式-5（x+y)+(x-y)+x(xy+y)的值 已知x+y=1,xy=-2,则x²y+xy²-2xy 1、(-7x^y)(2x^y-3xy^3+xy) 2、((x-y)^6)/((y-x)^3)/(x-y) 1-2/x+y=xy,4y+6x=xy.求xy的解? f(xy,x-y)=x^2+y^2+xy;f(x,y)/∂x;f(x,y)/∂y x-y/x+y=-1/2,x*x-xy-2y*y/x*x-3xy+2y*y的解是多少?同上,请将过程写出, 已知1/x-1/y=5,求分式y+xy-x/2x+7xy-2y的值. 已知1/x-1/y=5 求分式-x+xy+y/2x+7xy-2y 已知1/X-1/y=5,求分式(y+xy-x)/(2x+7xy-2y)的值 1/x-1/y=5求（-x+xy+y）/(2x+7xy-2y） x*x+xy=3,xy+y*y=2,则x*x+2xy+y*y=________? （x+2y-3xy)-(-2x-y+xy),其中x+y=1/2,xy=-1/2 因式分解（x+y-2xy)(x+y-2)+(xy-1)^2设x+y=a,xy=b, 已知xy/x+y=3,则代数式2x-7xy+2y/-x+xy-y的值是多少?