已知x^2-xy=21,xy-y^2=-12求x^2-y^2与x^2-2xy+y^2的值

已知x-xy =21,xy-y=-12,分别求式子x-y与x-2xy +y 已知x+y=1,xy=-2,则x²y+xy²-2xy 已知x-xy=8,xy-y=-9,求x+y-2xy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x:y=3:2,求(x²+3xy)/(xy+2xy) 已知xy为正整数,3xy=2x+3y+5.求xy=? 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=6,xy=7 求x^2y+xy^2=已知X+y=6,xy=7 x^2y+xy^2 已知x-xy=10,xy-y=2,则x-y=（ ）,-2xy+x+y=（ ）. 已知x-y=3xy,则2x+3xy-2y除以x-2xy-y=? 已知x+xy+y=3,则(3x+2xy+3y)/(2x+xy+2y)= 已知x-y=3xy,则2x+3xy-2y/x-2xy-y= 已知x-xy=20,xy-y=-10,则x-y=( ),x+y-2xy=( ). 已知x-xy=20,xy-y=12,则x-y= ,-2xy+x+y=