x/2-3y=0 y+4z=0 （y≠0）则x/2的值为（）已经知道是-12z 为什么?

{2x+y=10 {x-y+z=4 {3x-y-z=0 证明 ：x/(y+z)+y/(z+x)+z/(x+y)>=3/2其中 x,y,z>0 已知方程组2x-3y-4z=0和x+y+z=0,并且z≠0,求x：y与y：z 已知4x-3y-6z=0,x+2y-7z=0,xyz≠0,求x-y+2z/x+y-zx-y+2z分之x+y-z 2x+z=10 x+y-z=4 3x-y-z=0 已知方程组4x-3y-2z=0,x-3y+z=0,z≠0求x/z,y/z的值 若xyz≠0且4(x/z)-5(y/z)=-2,(x/z)+4(y/z)=3,求x:y:z 已知 (x+y-z)/z=(x-y+z)/y=(y+z-x)/x,且xyz≠0,求代数式 ((x+y)(y+z)(x+z))/xyz 分式加减法：已知x+y/z=x+z/y=y+z/x(x+y+z≠0）,求x+y-z/x+y+z 已知x+y/z=x+z/y=y+z/x(x+y+z≠0）,求x+y-z/x+y+z的步骤 已知x+y/z=x+z/y=y+z/x(x+y+z≠0）,求x+y-z/x+y+z的步骤 已知：x^2/(z+y)+y^2/(x+z)+z^2/(x+y)=0,求x/(z+y)+y/(x+z)+z/(x+y)的值. x^2/(z+y)+y^2/(x+z)+z^2/(x+y)=0,求x/(z+y)+y/(x+z)+z/(x+y)的值 已知x-y/x+y=y+z/2(y-z)=z+x/3(z-x),求证8x+9y+5z=0THX.. 已知x,y,z 大于0,x+y+z=2,求证 xz/y(y+z)+zy/x(x+y)+yx/z(z+x)大于等于2/3 如果|x+y+z-6|+|2x+3y-z-12|+|2x-y-z|=0求x,y, 三元一次方程x+y+z=0 4x+2y+z=3 9x+3y+z=6x+y+z=04x+2y+z=3 9x+3y+z=6 已知：4x-5y+2z=0 x+4y-3z=0则：(x*x+y*y+z*z)/(x*y+y*z+z*x)=____.