已知1/x+1/y=1/6,1/y+1/z=1/9,1/z+1/x=1/15,求xyz/（xy+yz+zx）的值

已知：2x+y=6,x-3y=1 求7y(x-3y)(x-3y)-2(3y-x)(3y-x) 已知x,y满足{x>=1,x+y 已知x,y满足{x>=1,x+y 已知x>1,y>1,x+y=6,求(1-x)(1-y)的最大值 已知3x+4y-6x-1-y=0,那么x-y=_______. 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:2x-y/x+y=1/5,求2x+5y/6x-2y的值 已知x×x×y×y+x×x+y×y+1=4xy,求x,y的值快 已知x,y是整数,且x(x-y)+2012y(x-y)=1,求x,y的值. 已知 x/(y+z)+y/(z+x)+z/(x+y)=1求 (x*x)/(y+z)+(y*y)/(x+z)+(z*z)/(x+y)=? 已知x²+y²+6x-8x+25=0,求（x/x²-y² - 1/x+y）÷y/y-x 已知x+y=-6求[(x+y)^2-(x-y)^2+2y(y-x)]*1/4y的值没分了 抱歉 已知:【(x²+y²)-(x-y)²+2y(x-y)】/4y=1,求4x/4x²-y²-1/2x+y 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=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=3:5 y:z=6:1,求x:y:z( ):( ):( ) 已知x+y=1,求x+y的最小值 已知集合A={(X,Y)| |x-a|+|y-1|