已知x-xy=8,xy-y=-9,求x+y-2xy的值还有：当（m+n)²+2取最小值时,求代数式m²-n²与2|m|-2|n|的值还有：已知m-n=4,mn=-1,求（-2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn)的值

已知x-xy=8,xy-y=-9,求x+y-2xy的值 已知2x+xy=10,3y+2xy=6.求4x+8xy+9y=? 1.已知x--xy=8,xy--y=--9,求x+y--2xy的值 已知x+y=12,xy=9,求(x+3xy+y)/(xy+xy)的值 已知xy/x+y=2,求代数式8x-5xy+8y/-x+3xy-y的值 已知x+y+yz=5,y+z+xy=8,x+z+xy=9,求x,y,z 已知(1/x)-(1/y)=5,求(6x+7xy-6y)/(8y-9xy-8y) 已知x^2-xy=4,y^2-xy=9,求代数式x^2-2xy+y^2 已知x^+xy=-5,xy+y^=8,求2x^-xy-3y^的值都是2次 已知x:y=3:2,求(x²+3xy)/(xy+2xy) 已知x^2-xy=5,xy-y^2=-3求3(x^2-xy)-xy+y^2 已知x^-xy=5,xy-y^=-3,求式子3(x^-xy)-xy+y^的值 已知x+y=8,xy=12求x^2+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) 已知xy/x+y=3,求代数式3x-5xy+3y/-x+3xy-y的值.已知xy/x+y=3,求代数式3x-5xy+3y/-x+3xy-y的值. 已知X+Y=3XY,求2X+2Y-XY除以X+Y+2XY的值,要算理.已知X+Y=3XY,求2X+2Y-XY除以X+Y+2XY的值,要算理. 已知:x+y=8,xy=12.求:1.x^y+xy^2.x^-xy+y^3.x-y的值