已知4x+5y-7z=0 x+2y-z=0,且xyz≠0,试求x²+2y²-6z²/2x²-9y²-4z²的值.

已知x,y,z,满足方程组x-2y+z=0,7x+4y-5z=0 已知4x-3y-6z=0,x+2y-7z=0,求5x+2y-z/2x-3y-10z 已知x.y.z满足x-2y+z=0且7x+4y-5z=0,求x:y:z的值 已知x、y、z满足x—2y+z=0 7x+4y—5z=0 ,求x：y：z 已知x,y,z满足方程组x-2y+z=0 7x+4y-5z=0求x:y:z的值 已知x+4y+3z=3x-2y-5z=0,求x+2y-z/2x-3y+7z的值 已知x、y、z满足{x-2y+z=0;7x+4x-5z=0,求x:y:z的值. 已知x,y,z满足方程组x-2y+z=0 7x+4y-5z=0,且z不等于0,2x²-3y²+z²/y²-2z²的值为? 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^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z不等于0,x、y、z满足4x-7y-5x=0,2x-y-z=0.求x：y 已知{x-5y+2z=0 3x-5y-4z=0,求x：y:z 已知x+4y-3z=0,4x-5y+2z=0,则x：y：z 已知2x+5y+4z=6 3x+y-7z=-4求x+y-z 已知方程组4x-5y+2z=0 x+2y=3z 则x:y:z 已知4X=7Y+5Z,2X+Y=Z,那么X:Y:Z的值是? 已知4X=7y+5z,2x+y=z,那么x:y:z的值是? 已知：4x-5y+2z=0 x+4y-3z=0则：(x*x+y*y+z*z)/(x*y+y*z+z*x)=____.