如果x/3=y/1=z/2,且xy+yz+zx=99,则x+2 y-3z的值为?

(x+y-xy)/(x+y+2xy)=(y+z-2yz)/(y+z+3yz)=(z+x-3zx)/(z+x+4zx),且2/x=3/y=1/z,则xyz=? 已知（x+y-xy）/(x+y+2xy)=(y+z-2yz)/(y+z+3yz)=(z+x-3zx)/(z+x+4zx),且2/x=3/y-1/z,则xyz=? 如果x/3=y/1=z/2,且xy+yz+zx=99,则x+2 y-3z的值为? 如果1=xy/x+y,2=yz/y+z,3=xz/x+z,则x的值? 若|x-3|+|y+2|+|2z+1|=0,求(xy-yz)(y-x+z) 若x,y,z都是正实数,且x^2+y^2+z^2=1,求证yz/x+xz/y+xy/z>=根号3 若x/2=1/y=z/3,且xy+xz+yz=99,求4x^2-2xz+3yz-9y^2的值. 分式题:xy=x+y,yz=2(y+z),zx=3(z+x),求xyz/(xy+yz+xz)xy=x+y,yz=2(y+z),zx=3(z+x),求xyz/(xy+yz+xz) 已知|x|=1,|y|=2,|z|=3,且xy＜0,xyz＞0,试求（x+y+z)×(xy+yz)的值. 已知X,Y,Z都是整数且xy+yz+zx=1,求证x+y+z>=根号3 若|x-3|+|y+z|+|2z+1|=0,求XY-YZ的值 若｜x-3｜+｜y+z｜+｜2z+1｜=0,求xy-yz的值 已知x,y,z∈R+,且x+y+z=3,求证：x^2/（y^2+z^2+yz）+y^2/(x^2+z^2+zx）+z^2/(x^2+y^2+xy)≥1 已知x:y=1:3,y:z=1:4,且x-2y+3z=62,多项式xy-yz+xz的值为 已知xy(x+y)^-1=1,yz(y+z)^-1=2,xz(z+x)^-1=3,试求xyz(xy+yz+xz)^-1的值 已知xy(x+y)^-1=1,yz(y+z)^-1=2,xz(z+x)^-1=3,试求xyz(xy+yz+xz)^-1的值 (x+y-xy)/(x+y+2xy)=(y+z-2yz)/(y+z+3yz)=(z+x-3zx)/(z+x+4zx),且2/x=3/y-1/z,则xyz=?看清楚是2/x=3/y-1/z 若x/3=y/1=z/2,且xy+yz+zx=99,那麽2x^2+12y^2+9z^2=?