已知x-y=1,xy=2,（-2xy+2x+3y）—（3xy+2y-2x）-（x+4y+xy）?主要是过程~谢谢,告诉我解这类题的方法谢谢~

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+1)²+|y-1|=0,求2(xy-5xy²)-(3xy²-xy)得值 已知x-xy=8,xy-y=-9,求x+y-2xy的值 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:(-2xy+2 x+3y)-(3xy+2y-2x)-(x+4y+xy)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 y=1,xy=-3,求2xy-4x 4(y-2(xy-x)) 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) 已知xy^2=-2xy(x^2y^5-xy^3-y) 已知x^2-xy=5,xy-y^2=-3求3(x^2-xy)-xy+y^2 已知x²+xy=2,xy+y²=1,求x²+2xy+y²的值 已知x+y=1,xy=1/5,则x^2y=xy^2 已知实数xy满足x²﹢y²-xy+2x-y+1=0求xy 已知x:y=3:2,求(x²+3xy)/(xy+2xy)