已知xy+x=-1,xy-y=-2,求代数式-x-[2y-2(xy+x）平方+3x]=+2[x+(xy-y)平方]的值,

已知1/x+1/y=3,求分式(3x-3xy+3y)/(x+xy+y)的值我知道第一步是两边都乘以xy得x+y=3xy,然后怎么代进去,求回答! 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(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x y=1,xy=-3,求2xy-4x 4(y-2(xy-x)) .已知:x-y=1,xy=-2.求:(-2xy+2 x+3y)-(3xy+2y-2x)-(x+4y+xy)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x²+xy=2,xy+y²=1,求x²+2xy+y²的值 已知实数xy满足x²﹢y²-xy+2x-y+1=0求xy 已知x^2-xy=5,xy-y^2=-3求3(x^2-xy)-xy+y^2 已知x:y=3:2,求(x²+3xy)/(xy+2xy) 已知x+y=1,xy=-2,则x²y+xy²-2xy 已知x+y=-1,xy=-2,求代数式-5（x+y)+(x-y)+x(xy+y)的值 已知xy为正整数,3xy=2x+3y+5.求xy=? 已知XY为正数,X+Y=1 求1/XY+XY的最小值