已知｛x+2y-9z=0,x-2y-5z=0｝,xyz不等于0,求2x的二次方+3y的二次方+7z的二次方/x的平方-4y的平方+9z的平方的值为多少?

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、y、z同时满足x+3y-5z=0,2x-y-3z=0,求x:y:z 已知｛2x-y-z=0,3x-9y+z=0求1,x:y:z 已知{x-5y+2z=0 3x-5y-4z=0,求x：y:z 已知x,y,z,满足方程组x-2y+z=0,7x+4y-5z=0 已知x+4y-3z=0,4x-5y+2z=0,则x：y：z 已知方程组4x-5y+2z=0 x+2y=3z 则x:y:z 已知(x+y+z)^2=x^2+y^2+z^2,证明x(y+z)+y(z+x)+z(x+y)=0 已知x、y、z满足方程组：x+y-z=6；y+z-x=2；z+x-y=0 求x、y、z的值 已知X.Y.Z满足方程组,X+y-Z=6y+z-x=2z+x-y=0求X.Y.Z的值 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 已知：4x-5y+2z=0 x+4y-3z=0则：(x*x+y*y+z*z)/(x*y+y*z+z*x)=____. 已知(x+y)(x+z)=x,(y+z)(y+x)=2y,(z+x)(z+y)=3z,求x,y,z 已知x+y-z=0,2x-y+2z=0 求（3x-2y+5z)/(5x-3y+2z)的值 已知x+y-7z=0 x-2y+5z=0(xyz不等于0）,求x+2y-z/y-2x+12z 已知4x-3y-6z=0,x+2y-7z=0,求5x+2y-z/2x-3y-10z 已知2x+2y-4z=0,2x+4y+5z=0,求x+y+z/x-y+z的值