已知x^2+y^2=2,xy=-1/2,求代数式(2x^2-y^2-3xy)-(x^2-2y^2+xy)的值 帮忙解答一下哈

已知x+y=1,xy=-2,则x²y+xy²-2xy 已知3/(x-y)=1/xy 求(-x-2xy+y)/ (2x+3xy-2y) 已知xy-x-y=11,求(xy-1)^2+(x+y-2)(x+y-2xy)的值. 已知xy/x+y=1/2,则代数式3x-5xy+3y/-x+3xy-y= .已知:x-y=1,xy=-2.求:(-2xy+2 x+3y)-(3xy+2y-2x)-(x+4y+xy)的值 已知x+y=-1,xy=-2,求代数式-5（x+y)+(x-y)+x(xy+y)的值 已知x-xy=8,xy-y=-9,求x+y-2xy的值 已知x+y=1,xy=1/5,则x^2y=xy^2 已知x y=1,xy=-3,求2xy-4x 4(y-2(xy-x)) 已知x+y=-1,xy=-2,求代数式-5（x+y)+(x-y)+2(xy+y)的值 由已知x+y=-2,xy=3那么2(x+xy)-[(xy-3y)-x]-(-xy)等于多少? 已知x(x-1)-(x²-y)=-3,求(x²y+xy²)÷xy-2y 已知x²+xy=2,xy+y²=1,求x²+2xy+y²的值 已知x-y=3,xy=1,求（-2x+2x+3y)-(3xy+2y-2x)-(x+4y+xy) 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 已知实数xy满足x²﹢y²-xy+2x-y+1=0求xy 已知xy^2=-2,求-xy（x^2y^5-xy^3-y)的值. 已知xy^2=-2 求-xy(x^2y^5-xy^3-y)