求x^2+xy-y^2和2x^2+xy+3y^的和

已知:x-xy=40,xy-y=-20,求代数式x-y和x+y-2xy的值. x-xy=40,xy-y= -20,求代数式x-y和x+y-2xy算试 若x-y=5,xy=6,求x^2-xy^2和x^2y+xy^2 求x^2+xy-y^2和2x^2+xy+3y^的和 已知整数x和y,满足x^+xy-2y^=7,求xy的值 已知 x+y＝4,xy＝2,求2xy+4xy+2xy x^2-xy/xy-y^2约分 y/x=ln(xy) 求dy/dx(xy-y^2)/(xy+x^2) 当x-y=2xy时,求4x-3xy-4y/xy 已知x-xy=8,xy-y=-9,求x+y-2xy的值 1-2/x+y=xy,4y+6x=xy.求xy的解? 3X^2+XY+Y=15 求XY. （x^2+xy/x-y)/（xy/x-y)计算 2x²y-3(2xy-xy)-xy 5xy^2-(3xy^2-(4xy^2-2x^2y))+2x^2y-xy^2求 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 y'=-2xy;求f(x).