已知2x^2+3y^2=6 ,求2x-y的最大值和最小值

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 已知：2x+y=6,x-3y=1 求7y(x-3y)(x-3y)-2(3y-x)(3y-x) 已知|x|=2,|y|=3,|x+y|=-(x+y)求x-y 已知xy=-2,x-y=3,求（x+y)（x-y)-y^2+（x-y)^2-（6x^2y-2xy^2)÷2y 已知x^2-y^2=6,x+y=3求x.y的值 已知x-2y=2,求4x-y-8分之3x+y-6 已知2y-x=-3,求[4y(2x-y)-2x(2x-y)]/(2x-y 已知X*X+Y*Y+6X-8Y+25=0 求（Y/X)+(X/Y)-2=? 已知(x+2y)(2x-3y)=y(y-4x),试求x/y的值 已知x-y=1,求[(x+2y)^2+(2x+y)(x-4y)-3(x+y)(x-y)]除以y的值大神们帮帮忙 已知x-y=1,求[(x+2y)²+(2x+y)(x-4y)-3(x+y)(x-y)]÷y的值 已知x≠y,x^2-x=y^2-y,求x+y的值. 已知x=3分之一,y=-2分之一,求代数式x-(x+y)+(x+2Y)-(x+3y)+(x+4y)...-(x+2009y) 已知x-3y=0,求(2x+y)/(x^2-2xy+y^2)X(x-y) 已知关于方程2x-3y=7,求3(y-7)-6(x-y) 化简求值：已知x、y满足：x^2+y^2-4x+6y+13=0 求代数式 的值.(3x+y)^2-3(3x-y)(x+y)-(x-3y)(x+3y)急用！