x△y=xy x▽y=(x+y)÷2 且(1△ 3)▽3=1△(3▽3)则(1△3)▽3等于多少?需要具体过程

|x|/x+y/|y|+xy/|xy|= x,y为正整数,且x^2-xy-2y^2=7,求x,y x,y为正整数,且x^2-xy-2y^2=7,求x,y 集合M={（x,y|xy>0,且x+y x,y 为任意实数,且x+y>=-2,且X+y+xy>=-1,则Y的最小值( ) x²-4y² x+2y---------- ÷ --------分数线x²+2xy+y² x²+xyx²-4y² x+2y----------÷--------分数线x²+2xy+y² x²+xy(x+2y)(x-2y)x(x+y)=----------------(x+y)(x+y)(x+2y)(x-y)x=------(x+y)这样对了吗? x,y都是自然数,且x(x-y)-y(y-x)=12,求x+y-xy的值 已知xy=-2,x-y=3,求（x+y)（x-y)-y^2+（x-y)^2-（6x^2y-2xy^2)÷2y (x+y)^2/y^2-xy÷[-y^2+xy/(x-y)^2,x=0,y=根号10 y均为正数,且xy=2x+y-1,则x+y的最小值 x=y且xy≠0.求1910x^2+99y^2/2009xy 已知x>0,y>0,且x+2y+xy=30,求xy的最大值 已知X>0,Y>0且X+2Y+XY=30求XY最大值 若x^2+y^2-2xy=49,且x>y,x+y=9,求xy的值 已知X.Y是正整数且XY+X+Y=23,x^2y+xy^2=120 已知xy≠0,且2x+3xy-2y=0,求(x+y)/(x-y)的值. f(xy,x-y)=x^2+y^2+xy;f(x,y)/∂x;f(x,y)/∂y 已知x>0,y>0,且x+6y=5根号xy,求(2x+根号xy-y)分之(x+根号xy+2y)的值