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

已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 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 x(x-y)2-(y-x)3 已知|x|=2,|y|=3,|x+y|=-(x+y)求x-y 已知x,y满x≤3,3x+2y≥6,3y≤x+9,则z=2x+y的最大值是 [2/3x-2/x+y(x+y/3x-x-y)]/x-y/x 化简：{2/3x-2/(x+y)[(x+y)/3x-x-y]}/(x+y)/x 计算2/3x-2/x+y(x+y/3x-x-y)/x-y/x 化简3x-2/(x+y)[(x+y)/3x-x-y]÷(x-y)/x 已知实数x,y满足,X-2y≥-4,3x-2y≤12,x+y≥2,则y/(x+1)的取值范围 已知x.y满足(x-y-2≤0,x 2y-5≥0,y-2≤0 则3x+y/x+1得多少 已知 2x-3y/y等于2 求x-y/2x 求x-3y/2x+y 已知2y-x=-3,求[4y(2x-y)-2x(2x-y)]/(2x-y 已知实数x,y满足条件x≥0,y≥x,3x+4y≤12,则(x+2y+3)/(x +1)的最大值是 [(3x+y)(x-y)-(2x+3y)(x-y)]*(x-y) 计算：x+2y/x-y+2x/y-x-3y/x-y 化简:(x-3y)(x+y)-(x-2y)(x+2y)-(x-y)平方