4x^2+y^2+xy=1 2x+y 最大值

(x+y)(x+y+2xy)+(xy+1)(xy-1)(x+y)(x-y)+4(y-1) 1-2/x+y=xy,4y+6x=xy.求xy的解? 分式x/2y,y/3x*2,1/4xy的最简公分母 x,y>0,且2/x+8/y=1,求xy的最值. (-2xy+2x+5y)-(3xy+2y-2x)-(x+4y+xy)其中x-y=4xy=-1 若x-y=4,xy=1,求(-2xy+2x+3y)-(3xy+2y-2x)-(x+4y+xy)的值 若x-y=4,xy=1,则(2x+y-2xy)-(3x+2y+xy)-(4xy+3y-5x)= x-y=1,xy=2.求：(-2xy+2x+3y)-(3xy+2y-2x)-(x+4y+xy)的值 .已知:x-y=1,xy=-2.求:(-2xy+2 x+3y)-(3xy+2y-2x)-(x+4y+xy)的值 化简求值x-4y/2x-7xy+3y×x-2xy-3y/2x+3xy-2y÷3x-6y/4x-4xy+y,其中：x=1999,y=-1 [(x+y)(x-y)-(x-y)^2-4xy]/2y,其中x=1,y=-1 求函数f(x,y)=e^-xy在闭区域{(x,y)│ 求函数f(x,y)=e^-xy 在闭区域{(x,y)│ x^2+4y^2≤1} 上的最值 已知x*x-4xy+4y*y=0 求[2x(x+y)-y(x+y)]/(4x*x-4xy+y*y)的值? 实数x、y满足方程x^2+4y^2-4xy+x-3y+1=0,求y的最值 (x^3+xy^2+1)/(x^3+xy^2-x^2y-y^3)×(x^2y-xy^2)/(x^3+xy^2-x^2y-y^3)+(x^2y+y^2)/(x^3+xy^2+x^2y+y^3)×(x^2y+y^3+1)/(x^2y+y^3-x^3-xy^2)+(x^3+y^3)/(x^3+xy^2+x^2y+y^3)简化为最简结果 已知x-y=3,xy=1,求（-2x+2x+3y)-(3xy+2y-2x)-(x+4y+xy) 若1/x-1/y=2,求3x-2xy-3y/x-xy-y的值3x-2xy-3y/x-xy-y 不好意思，是3x-2xy-3y/x-2xy-y x-2y=15,xy=-25,求x*x+4y*y-1