已知x,y满x≤2,2y≥x,2x+2y≥6,3y≤x+9,则z=2x+y的最大值是

x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 化简y(x+y)+(x+y)(x-y)-x^2 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 因式分解x(x+y)(x-y)-x(x+y)^2 (x+y)(x-y)-(x-y)^2如题 (x+y)(x-y)-(x-y)^2 【2(x-y)(x-y)(x-y)-8(x-y)(x-y)(x+y)+6y(x-y)(x-y)]/2(x-y)(x-y) 已知x+y≤5,2x-y≥4,求x+2y的最大值 已知x-y=3,求[（x+y)(x-y)-(x-y)^2+2y(x-y)]除以的值 已知3x =2y 求x/x+y+y/x-y-y²/x²-y² 已知x+y=a,2x-y=-2a,求[（x/y-y/x)/(x+y)-x(1/x-1/y)]/[(x+1)/y]的值 已知x≠y,x^2-x=y^2-y,求x+y的值. 已知x>0,Y>0,如何证x^2/y+y^2/x>=x+y 已知f(x+y,y/x)=x^2-y^2,则f(x,y)= x^2(x-y)+(y-x) x(x-y)2-(y-x)3 已知|x|=2,|y|=3,|x+y|=-(x+y)求x-y 计算:y-x分之x+y+x-y分之y-y-x分之2x-y 已知x,y满x≤3,3x+2y≥6,3y≤x+9,则z=2x+y的最大值是